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WHAT WE KNOW 



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OUTSIDE THE EARTH. 



BY ELIAS COLBERT, 

OF THE CHICAGO TRIBUNE, 

Emeritus Assistant Director Dearborn Observatory ; 
Author of "Astronomy Without a Telescope." 



PRICE, FIFTY CENTS. 



CHICAGO: - 
THE WESTERN NEWS COMPANY. 
I 871 . 

The Lakeside Press. 



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Entered according- to Act of Congress, in the year 1871, 

By ELIAS COLBERT, 
in the office of the Librarian of Congress, at Washington 



fi.^A^O 




220 



210 



200 



190 



180 



STAR-STUDIES. 



WHAT WE KNOW 



The Universe 



OUTSIDE THE EARTH. 






(BY E. COL(BE<HT, 

EMERITUS ASSISTANT DIRECTOR DEARBORN OBSERVATORY. 



CHICAGO: 

The Western News Company. 

1871. 



Astronomy is, at once, the oldest and the youngest of 
the sciences. The apparent movements of the lumina- 
ries and principal planetary bodies were observed, and 
their periods approximately known, in the earliest ages 
of the world's written history; while the vestiges of that 
primeval lore are deep-grained in the structure of the 
most ancient languages. Yet very little was known of 
the true plan or extent of the universe till after the inven- 
tion of the telescope — 263 years ago — and it is only 
within the present century that anything tangible has 
been reasoned out with regard to astronomy, except its 
mathematics. The greater portion of the chemistry of 
the science has really been developed within the past 
decade. So recent are many of the more interesting 
deductions that a great portion of even the reading world 
is ignorant of their character and importance. 

The following pages contain, in condensed form, the 
essence of this modern astronomy — at a price low 
enough to place it within the reach of the multitude — 
and although many facts previously stated are necessa- 
rily introduced, many others will be found here which 
are entirely new. The whole is an amplification of the two 
last of a course of lectures delivered by me, in February 
last, at Mattoon, 111. The first treats of the analysis of 
light, and the deductions made therefrom in relation to 
the chemical constitution of other worlds. The second is 
devoted to a consideration of the biological conditions 
obtaining on the sun, stars, and planetary bodies ; and 
sketches the past and future history of the universe, as 
indicated in the conditions of the present. E. C. 



STAE CHEMISTRY. 

Study of the light ray; velocity of light; wave motion. 
Polarization ; original and reflected light. Measuring 
the wave. The solar spectrum ; color due to wave 
length ; heat, light, and actinism. The fixed lines in 
the spectrum; their chemical relations; incandes- 
cence. Causes of bright and dark lines. Elements 
in the sun; their condition. Relative light, from 
sun, stars, planets, and nebulae. Connection between 
light and heat. Other spectra. Measure, and cause, 
of solar light and heat. Physical structure of the 
sun and stars. Sun spots and sun storms. Modern 
analysis of light. 

The most modern branch, of astronomical re- 
search is star chemistry : — a study which belongs 
almost exclusively to the present generation, 
though some of the basic principles employed in 
the investigation date back into the preceding 
century. Star chemistry indicates to us the 
conditions under which matter exists in the uni- 
verse around us ; as the mathematics teach us 
the relations of quantity — of matter or space. 

The various problems of celestial mensuration 
are all dependent upon one simple process. We 
find the direction which a ray of light makes, as 
compared with the direction of another ray, or 



4: THE LIGHT RAY. 

• with the line .of level at the place of observation. 
Two rays of light coming from a named celestial 
object, to two different points on the earth's sur- 
face, describe the unmeasured sides of a great 
triangle, which, when compared with a small 
triangle, enables us to state the distance of the 
object. And two rays, coming from opposite 
sides of the same object, and meeting at the eye, 
give us the principal sides of a reversed triangle 
which determines the actual magnitude of the 
celestial body. Similarly, the direction which a 
ray of light takes to-day, to meet the eye, com- 
pared with the direction of a like ray at any 
other observed time, furnishes us with all the 
evidences we possess in relation to the move- 
ments of those mighty masses, and the laws 
which govern those motions. 

All that we know of the universe, outside 
of our earth, and much of our knowledge of 
things terrestrial, has been obtained by the aid 
of light. A luminous ray, or a succession of 
rays, strike upon the eye — an organ furnished 
us for the express purpose of receiving the sen- 
sation of light — and we see ; we reason from 
these sensations, and then we know. 

Without any appreciation of the properties of 
this mysterious agent, which men call light, ex- 
cept its well-known property of moving in 
straight lines, we have reasoned out all the more 
important facts pertaining to the distances, 



VELOCITY OF LIGHT. & 

bulks, weights, and movements of the heavenly 
bodies. And there are very many other facts, 
equally interesting and important, which have 
been ascertained, during the past few years, 
through the same agency. We can reason out 
the conditions under which matter exists in 
other worlds, and trace their adaptability, or the 
lack of it, to sustain animated existences similar 
to those found on our own globe. But in order 
to comprehend the value of those deductions, it 
is necessary to know something of the nature of 
that force which lies at the foundation of all our 
knowledges, as it formed the basis of our being. 
The first, and greatest, in the recorded list of 
creative enactments was, not, let there be mat- 
ter, but, " Let there be light." 

The first great fact about light, is that it moves 
— occupying a measurable interval of time in pass- 
ing from place to place. Its velocity is so great 
that, for small distances, the sensation appears 
to be received without loss of time ; but the inter- 
val is appreciable for great distances. Von 
Eomer, a Danish astronomer, first observed 
that the eclipses of Jupiter's satellites appeared 
to occur about 16 minutes earlier when the 
earth and Jupiter are on the same side of the 
sun, than when on opposite sides of the lumi- 
nary. The difference in time has since been 
ascertained to be 16' 26". 6. This fact can only 
be accounted for by believing that the rays of 



6 LIGHT VIBRATION. 

light which leave the planet at the instants of 
apparent contact with his -moons, occupy nearly 
16i| minutes in traversing the whole diameter pf 
the earth's orbit, 182,865,700 miles. Dividing 
the distance by the time, we obtain 185,349.4 
miles per second, as the velocity of light. 

Light is immaterial ; not a substance, but a 
force. A tapping motion in the middle of the 
surface of a smooth sheet of water will cause a 
series of waves to form around the point struck, 
and the waves will spread outward in all direc- 
tions. If a light object be floating on the water, 
it will be moved up and down, but not outwards, 
by the undulation. This shows that the parti- 
cles of water do not move from centre to circum- 
ference with the propagation of the wave ; but 
that the particles set in motion at the centre 
move up and down, and that the movement is 
rapidly communicated to adjacent particles, 
lying outwards from the origin of the movement. 
The individual particles of water vibrate up and 
down, only ; and a cross section would show a 
movement at the surface like that exhibited by 
a rope, one end of which is fixed, and the other 
moved up and down rapidly. The sensation of 
light is communicated in this way, by a lumi- 
nous body-, in all directions ; and the surrounding 
air, or ether, is made to vibrate like the w^ater 
wave. 

But in order to represent the real character of 



POLARIZATION. 7 

the vibration produced by a ray of sunlight, we 
must consider it to be made in every direction — 
simultaneously — to the right and left, as well as 
up and down. The vibration of the ray is more 
like the movement of the surface of a muscle, 
which expands and contracts with the move- 
ment of the limb. Suppose we have a round 
cord of India-rubber, and alternately stretch it, 
and allow it to contract to its original length. 
As we extend the length of the cord it becomes 
thinner, and swells out as it shortens, equally on 
all sides. If we suppose this cord to represent 
the length of a single vibration of sunlight, 
the change in the outline — the changing distance 
of the surface of the cord from its central line — - 
will give some idea of the vibration of the light 
ray, in every direction. But when that ray 
of sunlight has struck upon a reflecting sub- 
stance, at a certain angle, and is reflected back 
to the eye, we find it to have lost this univer- 
sality of pulsation, and to vibrate only in one 
direction — as up and down, like the water sur- 
face. Light so changed is said to be polarized. 
The same effect is produced when we allow the 
ray to pass through a great number of sub- 
stances. If we take a thin plate of tourmaline, 
and hold it up in the path of a single ray 
of light, coming through a pin-hole into a 
darkened room, the ray will pass through it 
freely, and will also pass through a second plate 



8 LIGHT OF SUN AKD STARS. 

of tourmaline held symmetrically to the first; 
but if we turn the second plate a quarter round, 
the ray will not pass through it. The structure 
of the tourmaline may be represented on a large 
scale by a picket fence. We could shake a rope 
up and down between any two adjacent pickets ; 
and the wave motion of the rope would not be 
interfered with if passed between two fences, 
one built behind the other. But if the one set 
of pickets were perpendicular, and the other 
horizontal, the rope could not be vibrated. The 
tourmaline stops all the vibrations except those 
which are in the direction of its own grain ; it 
polarizes the ray. We find that all light coming 
direct from its origin, whether the sun, or a 
candle, is unpolarized. An instrument which 
enables us to tell whether a ray has been polar- 
ized, or not, is called a polariscope. 

When we examine the light coming from the 
fixed stars, through the polariscope, we find that 
it is unpolarized; the fixed stars shine by 
their own light, like our sun. But the same 
instrument shows that the moon and planetary 
bodies shine with a reflected light; the light 
coming from them is polarized ; it has been first 
received from the sun, and is then reflected 
to us. 

Two or more adjacent light waves coming 
from the same source, vibrate in harmony. But 
we can separate them by a simple device, and 



DISPERSION. 



cause them to travel over paths of unequal 
lengths ; then bring them together again, and 
thus measure the length of the wave. If we 




admit a ray of light through a pin hole, A, in a 
shutter, into a darkened room, and let it fall 
upon a sheet of paper at E F; then interpose 
an opaque cylinder at C, it may be thought that 
the whole space between the lines E and F will 
be darkened. But we really find that the space 
is divided up into a number of light and dark 
bands, the light doubling around the obstacle, 
as sound can be heard around a corner. The 
rays which meet in the middle, at B, have trav- 
ersed lines of equal lengths, and their vibrations 
are accordant at the point of meeting, producing 
light ; at the point H they have traversed paths 
of unequal length, so that the swell of one ray 
meets the reverse part of the other ray, and the 
interference of the vibrations takes away the 
effect of light, producing darkness, just as two 



10 LENGTH OF WAVE. 

non-coincident water waves would neutralize 
each other. At all the other light spaces the 
rays coming from opposite sides of the obstruc- 
tion have traversed unequal paths; but the 
difference of those paths is equal to the length of 
one or more vibrations, and the rays beat in 
unison, producing light. If we place an opaque 
substance so as to intercept the light, either 
above or below, the bands disappear; showing 
that both sets of rays are necessary to the 
production of the phenomenon. 

The following diagram represents the inter- 
ference of 
the rays, 

£~^"^ C and D, 

producing darkness; their vibrations destroy 
each other at the point of meeting. The lines 
A and B, 
having a 
difference 
equal to 

the length of one vibration, beat in unison at the 
point of junction, and produce light. We can 
calculate the relative lengths of the paths along 
which these rays have traveled, to agree or 
interfere with each other, and their differences 
will give the lengths of the wave pulsations 
of light. The average length of the wave of 
yellow light is about 22 of the parts obtained by 
dividing an inch into one million equal portions. 





THE SOLAR SPECTRUM. 



11 



There are about 45,000 pulsations in the length 
of a single inch. Wow, in each second of time 
light travels over 185,319.4 miles, or 11,713,- 
737,981 inches; therefore our light ray must 
make the inconceivable number of 530 million 
million pulsations in a single second. 

The ray of light is not a unit. Sir Isaac 
Newton discovered that a ray of sunlight may 
be artificially divided into the seven colors of the 
rainbow. If we take a triangular bar of solid 
glass, called a prism, and place that in the path 
of the ray coming through the small hole in the 

\ 



ACTINISM 




shutter, instead of the opaque cylinder, we find 
that the ray is split up ; and on the sheet of 
paper we obtain a beautiful elongated rainbow 



12 WAVE-LENGTHS. 

image. Examining it, we find that the several 
constituents of the solar ray are all bent at 
different angles from their former course, by 
passing through the prism. The red ray is least 
bent from the original course ; the violet is most 
largely deflected, or refracted, from the direction 
taken by the whole ray before it fell on the 
prism. The image thus formed is called the 
Solar Spectrum. 

Measuring each of these separated rays, by 
processes similar to that just referred to, we find 
that each has its own rate of vibration and wave 
length, the product of the two quantities being 
equal in each case. The extreme red is found to 
have 35,112 wave lengths to the inch ; and the 
extreme violet 64,020 lengths to the inch. The 
following are the corresponding numbers of 
vibrations per second, and length of wave, in 
decimals of an inch, at each end, and at the 
middle of the spectrum — the* junction of the 
green and the blue. 

Vibrations. Wave Lengths. 

Extreme Violet - - 751,840,000,000,000.- -.00001582. 

Middle - 606,285,000,000,000. - - .00001937. 

Extreme Red - - - 412,350,000,000,000. - - .00002848. 

These are exact measures. The numbers 
representing the wave lengths for the middle 
of each color are, approximately; Violet, 162; 
Indigo, 173; Blue, 186; Green, 202 ; Yellow, 
220; Orange, 212; Eed, 270; ten-millionths of 
an inch. 



DISTRIBUTION OF COLOR. 13 

The different colors of light are, therefore, 
considered to be due to the different lengths 
of the wave. 

The colors are not equally distributed. If 
we divide the visible spectrum into 360 equal 
parts we find the following to be the numbers 
representing the lengths of the different colors : 
Eed, 45 ; Orange, 27 ; Yellow, 48 ; Green, 60 ; 
Blue, 60; Indigo, 40; Yiolet, 80. We may 
reverse the analysis by a very simple process, 
and show that the blending of the rainbow 
colors in these proportions produces white light. 
On the flat side of the rim of a wheel paint the 
seven colors in spaces proportional to the above 
numbers ; if you turn the wheel round so rapidly 
as to prevent the colors from being seen sepa- 
rately, the painted rim will appear to be a 
pure white. 

It is a singular fact that, though the numbers 
we have given represent the limits of the visible 
spectrum, yet numerous experiments prove that 
the diffused rays extend some distance beyond 
the red, and reach out past the violet over 
a space many times greater than that occupied 
by the visible spectrum. We can see the spec- 
trum for some distance past the violet, by 
allowing the rays to fall on certain preparations 
made for that purpose. The visible spectrum is 
really the light -giving portion of the whole, 
which is found to exhibit three distinct, and 



14 



partially separate properties. If we hold a deli- 
cate thermometer in the path of the red rays, 
the instrument shows a rise of temperature, and 
the invisible rays beyond the red are more 
potential in the production of heat than those 
which are visible ; while scarcely any heat is 
manifested in the violet region. The solar ray 
is also a cause of chemical change ; a fact which 
is taken advantage of by the photographer in 
preparing his pictures. If we place a piece 
of paper, spread over with chloride of silver, in 
the spectrum, it is soon blackened, but not with 
equal rapidity in all portions. It changes color 
speedily in the violet region, and beyond it ; 
but changes very slowly if held among the red 
rays. The greatest amount of light is found 
near the middle of the spectrum. We can 
readily obtain from the solar ray two out of the 
three forces, heat, light, and chemical activity, 
isolated from the others. We can obtain heat 
without light by placing the thermometer be- 
yond the red end of the spectrum ; chemical 
action without light or heat, by placing a sensi- 
tized plate beyond the violet ; and light, almost 
without the other two, nearly at the junction of 
the blue and the green. We can not eliminate 
any portion of the effective properties of any 
part of the ray, but we can isolate one pulsation, 
or group of pulsations, from all the rest. 

The curved lines on the right hand side of the 



BLENDING OF KAYS. 15 

last diagram represent the relative intensities 
of these three forces in different parts of the 
visible spectrum ; the force being proportional to 
the distance of any point in the spectrum from 
the corresponding points in the curves. Thus ; 
the average light intensities for the several rays 
are, Bed, 94; Orange, 640; Yellow, 1,000; 
Green, 480 ; Blue, 170 ; Indigo, 31 ; Yiolet, 6. 
It was for a long time thought that the seven 
colors are, themselves, simple ; the well-known 
fading of one into the other, in the sjDectrum 
or the rainbow, being accounted for by the sup- 
position that the colors lap over each other near 
the places of junction. It has also been taught 
that there are only three primary colors — the 
red, the yellow, and the blue — all other colors 
and shades being produced by the admixture of 
these in various proportions. But the researches 
of modern science do not permit us to accept 
either of these theories. We find that the wave 
length varies gradually from one end of the 
spectrum to the other; and conclude that there 
are really thousands of waves concerned in the 
production of the spectrum, each giving a color 
of itself, distinct from all the rest, and having 
a wave-length measurably different from all 
its fellows. The blending of all produces white 
light ; the absence of all is darkness ; the union 
of many contiguous waves gives one of the 
seven prismatic colors. The ray of solar light 



16 THE SOLAR LINES. 

maybe regarded as a bundle of independent, yet 
connected immaterial pulsations, each of which 
has its own wave-length, by virtue of which it 
possesses individual powers for the production of 
the sensations of heat, color, or chemical action — 
named in the order of increasing refrangibility, 
and decreasing wave length. In passing through 
the prism these pulsations are separated, and 
made to diverge, so that they can be viewed and 
experimented on independently. We can not 
say " viewed separately," for it is not improba- 
ble that the single ray is composed of a greater 
number of pulsations than can be counted — 
just as the smallest living form is made up 
of millions of atoms of matter. 

If, instead of a round hole, we make a very 
narrow slit through which to admit our ray 
of sunlight, we find the dispersed image to 
be crossed, at irregular intervals, by fine, 
shadowy lines. Coming through the circular 
opening the dissected light is thrown on the 
spectrum in a series of circular patches which 
overlap each other, much in the same manner as 
a spread-out pack of cards will do, and thus pro- 
duces a partial blending of effects. The phenom- 
enon of overlapping is avoided when the slit 
is used. Dr. Wollaston first noticed this fact, 
distinctly, about the beginning of the present 
century ; and a German optician — named Fraun- 
hofer — mapped out the positions of 576 of 



SPECTRUM ANALYSIS. 17 

these lines about the year 1814, and designated 
some of the most prominent by the first eight 
letters of the alphabet. The number of lines 
in the solar spectrum is about 2000. Fraun- 
hofer afterwards examined the light coming from 
several of the fixed stars, and found different 
arrangements of lines from those noted in the 
sunlight ; l this was accepted as a conclusive 
answer to the charge that the dark lines are 
caused by the absorptive properties of the earth's 
atmosphere ; it was concluded that the cause of 
these diversities could only be found in the 
bodies examined — far outside the aerial envel- 
ope of our globe. This was really the first step 
in the spectrum analysis, which has since be- 
come so important a branch of research, and 
has opened up to the eyes of mortals the grand- 
est of truths, while it has placed in their hands a 
divining-rod with which to explore the most 
hidden mysteries of earth and heaven. 

In order to understand the value of this dis- 
covery it will be necessary to look at the chemical 
constitution of things on this earth. The material 
world appears to us under an endless variety of 
forms, but the skill of the chemist has shown that 
all are built up from a comparatively small num- 
ber (67) of substances, called elements. "We are 
acquainted with some of these elements, as iron, 
gold, silver, copper, and zinc, but the majority 
exist always in combination with others, and are 



18 THE SPECTRUM LINES I 

only isolated artificially. Thus : we do not find 
oxygen alone; but we meet with it mixed with 
nitrogen, to form the air we breat&e ; combined 
with hydrogen to form the water we drink ; 
with aluminum to form clay; with carbon in 
the breath we exhale from the lungs; with 
hydrogen and carbon to form sugar, and pure 
alcohol. Salt is not a simple substance, but 
is composed of two elements, named sodium and 
chlorine. ISTow, it is a singular fact that every 
one of these elements, when made to emit light, 
under certain conditions, gives a peculiar 
arrangement of lines in the spectrum, which 
is not given by any other element, and is given 
by itself, whether burned singly or in combi- 
nation, however intricate. "Whether we subject 
a drop of human blood, or a lump of salt, or 
a metal bathed in sea-spray, or any other of the 
shapes in which sodium is found, to the spectrum 
analysis, we equally find a double line, nearly in 
the middle of the yellow portion, which indicates 
the presence of sodium, however much it may 
be disguised to our senses, and though existing 
in the smallest possible proportions in the com- 
pound ; the double yellow line in the spectrum 
reveals its presence. The spectrum analysis has 
discovered to the chemist the existence of no 
less than five new elements — all previously 
unknown. 

The world principally owes to the labors of 



POSITION AND CHARACTER. 19 

Bunsen and Kirchoff, the development of the 
processes by which these facts have been use- 
fully applied to the study of astronomical 
physics ; though Angstrom, Roscoe, and Zollner, 
have also contributed largely to our fund of 
knowledge on this topic. They discovered that 
a burning, solid gives a continuous spectrum, 
unmarked by lines ; but that when the solid 
is reduced to the gaseous condition, the burning 
gas gives a spectrum (except under certain well 
understood circumstances) which is crossed by 
the bright lines characteristic of the substance. 
They next studied the image produced by the 
light of the burning solid and the burning gas 
combined ; the latter being placed nearest to the 
prism. They arrived at the remarkable con- 
clusion that the characteristic rays of the sub- 
stance, as given out by the solid, are neutralized 
by passing through the burning gas, which 
seems to be transparent to all but the character- 
istic lines given out by itself. The lines in the 
spectrum were faithfully reproduced ; but they 
were dark — just like those visible in the spectra 
of the sun and stars. 

The instrument us.ed in these investigations 
is called a spectroscope. 

It is found that most of the elements give 
more than one line — some of them very many 
— but whether few or many, the positions are 
always the same for the same elements. If 



20 LINES IN THE 

a single element be subjected to the test, the 
lines of that element are visible ; if a compound 
of two or more elements be examined, we find 
the lines which belong to, each of them. Hence, 
as a rule, the more complicated the substance 
analyzed, the greater is the number of lines 
visible at one time in the spectrum. Whether 
in combination, or apart, each element, when 
submitted to the spectrum test, gives indubitable 
proof of its presence, by the production of lines 
which are not given by other elements. It 
is, however, true that some of the elements 
interfere more or less with the lines of others, 
when in combination; the blue line of stron- 
tium disappears from the spectrum, if the 
chloride of that element be burned with the 
double chloride of copper and ammonium. We 
are not, therefore, justified in assuming that no 
elements are present in a burning body, other 
than those which give their fixed lines in the 
spectrum ; while we are warranted in believing 
that all those are present which show their 
characteristic bars on the ribbon of dissected 
light. 

The accompanying diagram shows the prin- 
cipal lines in this solar spectrum ; it would not 
be possible to represent the whole of the 2,000 
lines, or more, on so small a scale. The lines 
0, F, and H, are those which show the presence 
of hydrogen. The line D, is double, falls in the 



SOLAE SPECTRUM. 



21 



VIOLET END. 



middle of the yellow, and is the 
well-known sodium line. Iron 
makes itself known by a group of 
seven lines, of which E is the prin- 
cipal one, by a smaller group just 
below F, and two lines at Gr. Mag- 
nesium is indicated by three lines 
at b; and Nitrogen by two lines 
Q nearly half way between b and F. 
The solar spectrum contains the 
lines which indicate that the follow- 
ing elements exist in the Sun, in a 
state of incandescence: Sodium, 
iron, hydrogen, calcium, barium, 
F chromium, nickel, copper, magne- 
sium, cobalt, zinc, cadmium, man- 
ganese, aluminum, strontium, tita- 
i nium, gold, and potassium (18). Of 
: these, cobalt, strontium, cadmium, 
and potassium are regarded as not 
clearly shown to exist there. Other 
D metals may exist in the Sun, but, 
if so, in smaller proportions in the 
atmosphere, or in larger quantities 
c but not vaporized. Hydrogen,which 
b is the lightest of our known gases, 
a and is now believed to be a metal 
A at extremely low temperatures, is 
present in very large quantities. 
No trace of oxygen has yet been discovered in 



22 • ELEMENTS IN THE SUN 

the sunlight : if that element exists in the Sun it 
must be in very much smaller quantities than on 
the earth, as if present in considerable propor- 
tion it would undoubtedly exist in the gaseous 
surrounding, as in the case of our earth. 

From these facts we are enabled to draw the 
following important conclusions : 

The Sun is composed of the same materials 
as those which form a large proportion of the 
matter which makes up the bulk of our earth, 
and of all that exists on its surface ; while, yet, 
some of the most important of our earth elements 
appear to be absent. 

The Sun is intensely hot. The heat at his 
surface must be at least as great as that which 
attends rapid combustion here ; because the fixed 
lines in the spectrum appear only when the 
body examined is at a very high temperature. 

The heat at the solar surface is great enough 
to reduce to a state of vapor many of the ele- 
ments which are fusible only with great difficulty, 
by the aid of the greatest heat we can produce 
artificially. The vapor of iron which is detected 
in the Sun's atmosphere, necessitates a tempera- 
ture of not less than 4:500° Fahrenheit. 

The Sun is a globe of incandescent solid or 
fluid matter, surrounded by an incandescent 
atmosphere. The lines in the solar spectrum 
would not be dark, if it were otherwise. In this 
interior mass — the Sun proper — a great num- 



PHYSICAL CONDITION. 23 

ber of chemical elements may exist which do not 
yield up vapor to the surrounding atmosjjjiere, 
just as there are elements nrthe earth's structure 
which are not found in our air ; but those ele- 
ments which are gaseous with us, would most 
probably be apparent in the solar spectrum if 
they existed in the Sun. All the elements thus 
far traced in the Sun exist within as incandescent 
solids, or fluids, and without as incandescent 
gases. We* shall see presently that the Sun's 
interior is necessarily fluid — rendered so by 
intense heat. 

The spectroscope enables us to ascertain that 
this incandescent atmosphere extends to a dis- 
tance of five to six thousand miles from the Sun's 
surface. This shell of incandescent gas is called 
the chromosphere. 

[In an article in the March, 1871, number of 
the " Lakeside Monthly," I wrote as follows :] 

" Outside of this another phenomenon is visi- 
ble during a total eclipse of the sun. It is the 
corona (crown), which resembles the halo some 
of our painters have depicted round the heads of 
the saints. The shape and extent of the corona 
are not the same in all total eclipses of the sun ; 
in August, 1869, it was nearly twice as broad as 
in December, 1870. The limit of breadth of the 
true corona appears to be from one-fifth to two- 
fifths of the sun's apparent diameter. The solar 
diameter being nearly 853,000 miles, two-fifths 



24 THE SOLAR CORONA: 

of this quantity is about 340,000 miles, which is, 
appufcri'mately, the greatest breadth of the true 
corona — that which* gives in the photograph an 
evidence of its existence. 

" Very recently it has been surmised that the 
coronal display is caused by the reflection of the 
sunlight from numberless planetoidal chunks or 
specks of matter, which are either revolving 
around the central luminary in very small orbits, 
or else are falling to his surface to keep up the 
supply of light and heat at the centre of our 
system of worlds. This proposition is absurd. 
By means of the third law of Kepler — that the 
squares of the times are proportional to the cubes 
of the distances — we can easily compute that a 
mass of matter 350,000 miles distant from the 
sun's surface, must revolve around him once in a 
little less than seven hours (6.87) to preserve its 
orbit. That is, the mass of matter in question 
would swing round the sun nearly ninety times 
while the sun turns once on his own axis. Now, 
all the analogies of the system, and the very laws 
of motion, as we understand them, teach that a 
body revolving around the sun must have a less 
angular velocity than the sun ; and that if the 
angular velocity be the same, it is already a part 
of the sun. The corona can not, therefore be 
produced by reflection from bodies, whether large 
or small, moving in an orbit. We need scarcely 
to refer to the other branch of the theory. To 



ITS CHARACTER AND CAUSE. 25 

suppose that matter wliicli once circled around 
him, is continually falling to the sun in sucli 
immense quantities as would be necessary to pro- 
duce this phenomenon whenever an eclipse per- 
mitted us to see it, would be to suppose that the 
solar system is in a state to which a galloping 
consumption is but a snail's march ; it is simply 
impossible. 

"Our atmosphere is usually spoken of as 
lying within forty-five or fifty miles of the 
earth's surface. Now, observations made of the 
height of the aurora polaris of August 28, 1859, 
at several stations situated on a line extending 
from the West Indies to Maine, showed that 
the aurora formed a stratum of light extending 
from forty-six miles to five hundred and thirty 
miles above the surface. The aurora is now 
known to be due to an illumination of atmos- 
pheric particles by electric excitation, just as the 
rainbow is produced by the sunlight reflected 
from the rain-drops. The auroral display is 
believed to be seldom visible at a less elevation 
than forty-five miles. In other words, it is only 
produced by the operation of the electric force 
on matter so extremely tenuous that a globe of 
it, the size of our earth, would not weigh a single 
ounce. And it is easy to calculate that the 
atmosphere extends much further than the visible 
limits of the aurora. The rotary motion of the 
earth on her axis gives a centrifugal motion 
2 



26 the corona; and 

which destroys one part in two hundred and 
eighty-nine of the weight of a body at the Equa- 
tor, and we must rise to a height of twenty-two 
thousand miles above the surface before we come 
to a point where the attraction of gravitation to 
the earth would be completely balanced by the 
centrifugal motion. Inside of this limit, a body 
must pass round the earth more rapidly than 
once in twenty-four hours to avoid falling to her 
surface. Outside of those limits, a body must 
move more slowly than the earth's axial velocity 
in order to retain its distance. That distance is, 
therefore, the limit of the earth as an integral 
mass. All within it necessarily belongs to the 
earth, and the process of expansion must proceed 
from the surface to that point, before we leave 
the attenuated atmosphere and find ourselves 
fairly launched into the regions of space. The 
air is sufficiently dense to be susceptible of illu- 
mination, only to a height corresponding to one 
part in forty-two of this distance. 

" Computing the sphere of the sun's attraction 
on the same principle, we find that it extends a 
little more than fifteen millions of miles from his 
surface. The same ratio as obtained in the case 
of the earth (1-42) will give 368,000 miles from 
the sun's surface for the limit of the true corona, 
or 13f minutes of arc at the sun's mean distance. 
My sketch of the corona during the eclipse of 
1869, made at Des Moines, Iowa, shows the 



AUKOKA POLARIS. 27 

corona to have extended to about this distance 
all around the sun. It seemed to extend a little 
further than this in one or two directions, in 
pointed rays of hazy light ; that was undoubtedly 
the result of earth atmospheric conditions. 

"We have here a precise analogy between the 
conditions of the earth and sun, which warrants 
us in concluding that the corona is a genuine 
solar phenomenon ; and that, whether the portion 
nearest to the disc be self-luminous or not, the 
exterior portion, to a distance of not more than 
368,000 miles, is produced by the reflection of 
solar light from a solar atmosphere. 

"But there is one other point of similarity 
between the two sets of conditions in earth and 
sun, which tends to establish the conclusion I 
have essayed to deduce. It is that the corona 
gives a line in the spectrum wdrich corresponds 
with the division of 1474 in Kirchoff 's scale, and 
is not given by the burning of any chemical 
element with which we are acquainted, but is 
seen in the spectrum of our aurora polaris. In 
both cases this indicates the existence, in the 
higher regions of the atmosphere, of an element 
w T hich is probably distinct from all those known 
to us, and takes the more elevated position by 
virtue of its less specific gravity ; as hydrogen 
takes an exterior place in the sun for the same 
reason, and as it possibly does in our atmosphere, 
though the fact has not yet been accepted. We 



28 THE LATE ECLIPSE : 

have no warrant for supposing that this, or any 
other line, gives ns a trace of that mysterious 
ether which fills all space not occupied by denser 
matter ; that ether is too much attenuated, and 
too cold by reason of that attenuation, to give 
the semblance of a line in the spectrum. 

"A very interesting observation was made by 
Professor Young during the eclipse of Dec. 22, 
1870. Directing his spectroscope to the eastern 
edge of the sun, just as the advancing moon 
touched it at the beginning of the total phase, 
the dark lines in the spectrum suddenly died out, 
leaving the continuous spectrum, which had 
never been seen previously except by Secchi, the 
eminent Italian astronomer. This condition 
lasted but for an instant, and then the lines 
which were dark in the ordinary spectrum sud- 
denly became bright, and continued so for one 
or two seconds of time. Now this latter fact not 
only proves that the theory of Kirchoff is true 
— that the dark lines are due to the incandes- 
cence of a solid or liquid, on which is superposed 
an incandescent gas — but it also leads to the 
valuable deduction that the space of about four 
hundred miles in depth at the base of the chro- 
mosphere is the only one which contains all the 
elements the existence of which in the sun is 
revealed by the spectrum analysis. 

" I conclude, therefore, that the facts in regard 
to the constitution of the sun are as follows : 



ITS TEACHINGS. 29 

" First. The sun consists of an incandescent 
liquid mass, corresponding to the liquid interior 
of our own globe. That mass — the dimensions 
of which are usually accepted to be those of the 
sun itself — contains eighteen chemical elements 
known to us, and probably many more, the exist- 
ence of which is not shown, because they do not 
also exist in the gaseous condition outside. Our 
earth's interior may contain several elements 
which have never been met with on the surface. 
If the solar system originally formed one vast 
mass, which was afterwards separated into 
numerous bodies, it is but reasonable to suppose 
that the central orb contains most of the ele- 
ments found in the planets, and some which are 
peculiar to himself. 

" Second. This more dense fluid mass is sur- 
rounded, to a depth of some four hundred miles, 
by an incandescent gaseous envelope which cor- 
responds in position to our earth's crust. This 
envelope contains about eighteen of the chemical 
elements which exist within ; and its superposi- 
tion on the central mass is the cause of the dark 
lines in the solar spectrum. 

" Third. This shell is surrounded, to a depth 
of five or six thousand miles, by the true chro- 
mosphere, which corresponds to our ocean, and 
contains but five or six of the elements, of which 
hydrogen appears to be most abundant — all in 
an incandescent state. 



30 SOLAR ATMOSPHERE. 

" Fourth. A non-luminous envelope, corre- 
sponding in position and function to our atmos- 
phere, which is dense enough, for a height of 
nearly four hundred thousand miles, to reflect 
the light emitted from the incandescent interior. 
This reflected light is too feeble to be appreciable 
by us in competition with the glare of the direct 
sunlight ; but is visible when that direct sunlight 
is cut off by the interposition of the moon. Yast 
masses of hydrogen, and the other components 
of the chromosphere, shoot up into this envelope, 
as the waves of ocean dash up into our atmos- 
phere, and are carried above the normal surface 
in a way which finds a feeble analogy in the 
cloud formations of our atmosphere from the 
waters beneath. The light reflected from this 
envelope all gives evidence of polarization, except 
that coming from the portion immediately adja- 
cent to the chromosphere. The latter undoubt- 
edly both emits and reflects light. 

" Fifth. The extent of the coronal display, 
during a total eclipse of the sun, corresponds to 
the relative intensity of the convulsions occurring 
nearer the normal surface, which are gauged to 
us by the comparative extent of the sun spots, 
and the magnitude of the rose-colored protuber- 
ances visible during the total eclipse, and the 
faculae which are seen at other times in the tele- 
scope. As these latter phenomena of solar vari- 
ability are now identified with the positions 



MEASURE OF SUN LIGHT. 31 

presented by planetary revolution, the extent of 
the corona is referable to the action of worlds 
outside the sun, just as the intensity of our auro- 
ral exhibitions is also known to be associated 
with, and due to, the same agencies. The solar 
corona and the Telluric aurora are, therefore, not 
only as nearly identical in character as is possible 
under such widely different sets of conditions ; 
but both vary in the same ratio as their same 
exciting causes." 

It is very seldom that we can bear to look at 
the Sun with the naked eye. Only when his 
rays have to pass through considerable quanti- 
ties of cloud vapor before reaching us, can we 
view him without the aid of smoked or colored 
glasses, to modify the effects of his blinding glare. 
The most intense lights we can produce artifi- 
cially, are nothing as compared with it. The 
most brilliant artificial light, the calcium, pro- 
duced by a ball of quicklime, on which a mix- 
ture of ignited oxygen and hydrogen gases is 
kept constantly playing, can not be looked at 
without injury to the eye, if brought near enough 
to appear of the same size as the Sun. But if 
the calcium light be placed between the eye and 
the Sun, and both be observed through a colored 
glass, the calcium light looks black by compari- 
son. Sir John Herschel estimated that the Sun 
gives out as much light as 146 balls of calcium, 
each the size of the Sun, would give, if removed 
to the same distance from us. 



32 COMPARISON OF 

Let us take as the unit of light measurement, 
the faintest star which is distinctly visible to the 
naked eye on a clear night. There are about 
4424 such stars, classed as of the 6th magnitude. 
There are 959 stars, each of which gives twice 
as much light as this unit, and are classed as of 
the 5th magnitude. In the order of 4th magni- 
tudes we rank 327 stars, each giving 6 units of 
light. In the 3rd magnitude there are 141 stars, 
each giving 12 units of light. Of the 2nd 
magnitude there are 34, each giving 25 units of 
light ; and of the 1st magnitude there are 20, 
each of which gives 100 or more units of light. 
Strictly speaking, there are very few stars of 
equal brightness, but it is found convenient to 
classify them as nearly as possible to these aver- 
ages. Sirius gives 320 such units of light, and 
Alpha Centauri, the brightest star in the South- 
ern sky, except Canopus, and the one which is 
believed to be nearest to our Sun, gives eighty 
times as much light as an average star of the 6th 
magnitude. The light given to us by the plane- 
tary bodies varies widely with their distances 
from us. We may represent the averages by the 
following numbers : Uranus, 1 ; Saturn, 25 ; 
Jupiter, 250 (sometimes 500) ; Mars, 30 ; Yenus, 
160 (sometimes 600) ; and Mercury, 6. Now, 
if we add all these together, and allow 4000 
units for the filmy light received from the milky 
w T ay, and other stars too faint to be individually 



SUN AND STAR LIGHT. 33 

visible, we shall only have about 20,000 units, 
or 200 times as much light as is given us by an 
average star of the 1st magnitude. 

The light of the full Moon is estimated to be 
9,400 times greater than that received from 
Sirius, or 3,000,000 times our unit, or 150 times 
as much as we should receive from all the planets 
and stars together, if they were all above the 
horizon at one time. But the light of the Sun 
is computed to be 547,500 times greater than 
that of the full moon, or equal to that of 
(1,612,500,000,000) more than one and a half 
million million stars of the 6th magnitude, or 
8,212,500 times greater than that of all the 
planets and stars together. We receive sixteen 
million times as much light on a clear day, as on 
a star-lit night when there is no moon. 

And yet we have good reason to believe that 
very many of those shining bodies, which con- 
tribute such infinitesimal proporjons tc the light 
and heat we receive on this Earth, ai 3 much 
larger than our Sun, and radiate many times 
more heat into space than does the centre of our 
system. The light of the Sun is about ten 
thousand million times greater than that of 
Sirius, but if the star were brought as near to 
us as is the Sun, we should receive nearly eigh- 
teen hundred and ninety thousand million times 
more light from him than now ; and we find in 
this way that Sirius gives off one hundred and 



34 STAR DISTANCES. 

ninety-two times as ranch light as onr Snn; 
whence his diameter must be fourteen times 
greater, and his volume 2688 times larger, if the 
light of both be equally intense for each square 
yard of surface. 

Contrast with this the light of the nebulous 
clusters which are visible only in the telescope. 
Their light has been estimated to range from 
tto "o to -g-owo of that of a sperm candle at the 
distance of one quarter of a mile from the eye. 

We have already seen that light travels at the 
rate of 185,349.4 miles per second. Yet with 
this velocity the light which an inhabitant of the 
Southern hemisphere receives on his eye from 
Alpha Centauri, left that star nearly 3|- years 
previously. It is estimated that, on an average, 
light requires 15^- years to reach us from a star 
of the 1st magnitude ; 28 years from a star of 
the 2nd magnitude ; 43 years from a star of the 
3rd magnitude ; 120 vears from a star of the 
6th magnitude, and 60,000 years from some of 
the faint nebulae to which we have just now 
referred. Though only a faint glimmer of light 
is able to struggle into view from these shadowy 
masses, in the telescope, yet these nebulous clus- 
ters of matter must be immense to be visible at 
such great distances. The nebula in the sword 
of Orion can scarcely be less than 100 times the 
diameter of the whole orbit of J^eptune ; and 
the nebula in Andromeda has a diameter fully 



LIGHT AND HEAT. 85 

three times greater than that of Orion. The 
nebula of Andromeda is at least eight hundred 
thousand million miles in diameter, and a beam 
of light would occupy more than two months in 
passing through it ; the dimensions of the nebula 
may he even 400 times that immense number. 

Light and heat are co-ordinate ; but they do 
not always correspond in intensity, as we have 
already seen in looking at the several divisions 
of the solar spectrum. If we compare the 
results of combustion in the case of hydrogen 
and carbon, we find that hydrogen gives out the 
most heat of the two, for equal weights burned. 
So with the stars ; which, though not necessarily 
burning, in the sense in which substances burn 
on this earth, are yet all in a fervid glow, — 
heated so highly that nothing with which we are 
acquainted could retain the solid form if trans- 
ported to one of those incandescent masses. 
The great majority of the bodies we see are 
intensely hot ; too hot to permit vital existence, 
as we understand it, upon their surfaces. But 
we must remember that at the distance of Sirius, 
the Earth, and other planets of our system, 
would be invisible. Each of those stars, like 
our Sun, may be a centre of light and heat to 
a family of worlds, though we see them not. 

A very good idea of the connection between 
light and heat may be obtained from viewing 
the successive phenomena produced by the grad- 



36 CHEMISTRY OF 

ual heating of a bar of metal in the fire. A 
piece of iron, heated to the point of boiling 
water, emits rays which can be felt by the hand, 
though invisible to the eye. At the temperature 
of 977° the rays become visible — the iron 
appears red ; and if we place it before the prism 
the red rays appear in the spectrum, unaccom- 
panied by other colors. As we increase the 
temperature from this point the color of the 
iron changes, and the different hues appear con- 
secutively in the spectrum ; successively, counting 
from the red end, till at the temperature of 
2130° all the colors appear at the same time, 
and the iron becomes white hot, the whiteness 
being due to the blending of all the rays, which 
are individualized in the spectrum. At still 
higher temperatures the color is white, showing 
that all the prismatic hues are given out at any 
temperature over 2130°, at the same time; but 
the chemical activity of the rays beyond the 
visible violet is heightened, and increases with 
the heat imparted to the iron, which must be 
raised to a very much higher temperature in 
order to prolong the chemical rays to the same 
distance as in the Solar spectrum. The charac- 
teristic lines of the iron appear in the spectrum, 
successively, in the same order. We arrive at 
the singular conclusion that the greatest chemi- 
cal activity, and the darker colors, are only pro- 
duced by the most intense heat ; and that if the 



SUN AND STAR LIGHT. 37 

Sun were only as hot as melted iron there would 
be but very little chemical change possible on 
the Earth's surface — no growth of vegetables or 
flowers, or flesh and blood — no vegetable or 
animal decay. The heat rays are really those 
given out at comparatively low temperatures. 

In this fact we have a means of forming some 
idea of the comparative temperatures of the 
stars. Those which give out rays in which the 
red predominates, as Aldebaran, Betelgueuse, 
and Antares, are perhaps relatively cool bodies ; 
and the white stars, as Polaris, Regulus, Dene- 
bola, and Fomalhaut, are among those which 
give out the most light, are the hottest, and their 
attending planets are those among which the 
most rapid changes take place, owing to the 
greater amount of chemical activity developed. 

We may dwell a little longer upon the spec- 
trum, and find that it has still many secrets to 
reveal. We turn our instrument to the stars, 
and we find that they all, like our Sun, contain 
elements which are found on the earth ; but that 
the exhibited elements are not the same in all. 
In the spectrum of Betelgueuse, we have lines 
which show the presence of sodium, magnesium, 
calcium, iron, and bismuth, in the star. In the 
light of Sirius we find the lines which tell of 
sodium, magnesium, iron, and hydrogen. In 
Pollux and Yega we have evidences of the exis- 
tence of sodium, magnesium, and iron. Aldeb- 



38 STAR COLORS. 

aran has hydrogen, sodium, magnesium, calcium, 
iron, bismuth, antimony, and mercury, with the 
element called tellurium, which was so named 
from Tellus (the earth) on the supposition that it 
is peculiar to our globe. There is no tellurium 
or bismuth in the Sun. Hydrogen, which is 
present in such vast quantities in the Sun, and 
on the Earth, is not found in Betelgueuse. 

The spectroscope also enables us to find rea- 
sons for the different colors of stars, in the special 
arrangements of lines in their spectra. Thus: 
Our Sun, Pollux, Capella, and Tarazed, are yel- 
low; giving but few dark lines in the yellow por- 
tion of the spectrum, to interfere with the full 
effect of the yellow ray. Ras Algethi (Alpha 
Herculis) is an orange-colored star, because it has 
few shadowy lines in the yellow and orange por- 
tions of the spectrum ; the great majority of the 
lines falling in the green, the blue, and the red. 

If we direct the spectroscope to the nebulae, 
we find some startling differences. Some of them 
exhibit a spectrum analogous to those of the fixed 
stars, showing that they are composed of aggre- 
gations of luminous bodies too far distant to be 
individually visible. But we find that the spectra 
of many nebulae are made up of but one color, 
crossed by two or three bright lines. "We have 
already seen that the bright line is produced by a 
glowing gas,without an incandescent solid or liquid 
mass behind it, or in its interior ; and in this 



THE NEBULA. 39 

peculiar spectrum we find not only a proof that 
these nebulae are only aggregations of gas, or 
cloudy matter, but a fact which overthrows a 
theory till recently thought to be well established. 
It had been found that the higher the power of 
the telescope employed in looking at these shad- 
owy masses, the greater was the number of those 
resolvable into small stars ; and it was inferred 
from this, that all those nebulae which appeared 
only as films in the field of the best telescope, 
were simply assemblages of stars too remote to 
be seen distinctly. But we now know that many 
of these masses are not, and never were, stars ; 
though they may become such in the far distant 
future : in the same way as our solar system is 
believed to have been condensed from a globular 
mass which once filled the whole space now 
bounded by the orbit of Neptune, and had then 
a density 200,000,000 times less than that of 
hydrogen. The lines in the spectra of these nebu- 
lae lead us to infer that they are largely composed 
of hydrogen and nitrogen. It has also been 
found by recent observations that some of these 
true nebulae change their apparent places much 
more rapidly than the fixed stars in their imme- 
diate neighborhood. This fact indicates that the 
nebulae are much nearer to us than the stars. 
Indeed, it has recently been asserted that many 
portions of the milky way are much nearer to 
ns than the stars which obscure the brightness of 
that brilliant belt in their apparent vicinity. 



4:0 THE COMETS. 

Looking at tlie comets through, the spectro- 
scope, we find that they, too, are masses of vapor; 
a fact apparent, also, in their comparative absence 
of weight when balanced against the planets and 
their moons. Incandescent carbon, in more than 
one form of chemical combination, is believed to 
be the principal element in many of the comets. 
The spectroscope fails to inform ns with equal 
distinctness of the composition of the Moon and 
planetary bodies, because the light we receive 
from them is only reflected sunlight. But a com- 
parison of the same sunlight, as reflected from 
different bodies, enables us to draw many valua- 
ble inferences respecting the character of their 
atmospheres, and to see that the Moon has no 
atmosphere — there is neither water nor air on 
the Moon's surface. 

"We have seen that the Sun and stars are 
intensely hot. Have we any means of answer- 
ing the question, how hot is the Sun? and thence 
of forming an idea of the temperatures of the 
stars ? 

The experiments of Pouillet (a French philos- 
opher) with the lens pyrheliometer, show that 
the heat annually received from the Sim by our 
Earth is equal to that required to melt a layer of 
ice 101 feet in thickness ; and that the heat 
received from space would melt another layer of 
ice 82 feet in thickness ; only a very small pro- 
portion of the latter coming from the stars. The 



HOW HOT IS THE SUN ? 41 

heat annually received, therefore, averages that 
required to raise the temperature of 183 feet of 
ice through 140°. This melting power is evi- 
dently expended on every point of the surface of 
a hollow globe surrounding the Sun at the same 
distance as the Earth ; the total area of such a 
globe would be 2,127,000,000 times the area of a 
great circle of the Earth. The Sun gives off 
2,127,000,000 times as much heat as would be 
required to melt an ice envelope, 101 feet in 
thickness, all around the globe. In other words, 
each square foot of the Earth's surface receives 
from the Sun, every hour, enough heat to raise 
the temperature of one pound of water 100°. 
Now, if we should reason from this that the heat 
increases as the square of the distance from the 
Sun decreases, then, the distance from the Sun's 
centre to his circumference being only 2l ^ that 
of the distance to the Earth, the square of this 
number, nearly 46,000, would be the ratio ot 
heat given off from every square foot at the 
Sun's surface; equal to 4,598,940° per hour, or 
76,649° per minute. The heat at the Sun's sur- 
face would raise one pound of water 1277.5° in 
temperature each second, on each square foot of 
the Sun's surface. The ratio being 46,000 ; then, 
if the Earth's average temperature be taken at 
58°, it might be thought that the Sun's tempera- 
ture is 58x46,000, or 2,668,000°. 

By reasonings similar to this, Pouillet has esti- 



4:2 PHENOMENA AND 

mated that the heat at the surface of the Sun is 
sufficient to melt daily a layer of ice 10^ miles in 
thickness ; Sir John Herschel estimates that the 
heat emitted hourly is equal to that which would 
be produced by the combustion of six tons of coal 
on every square yard of his surface, and assumes 
that the heat is sufficient to keep melting a cylin- 
drical pillar of ice 45 miles in diameter, fed into 
the Sun with the velocity of light. Dr. J. B. 
Mayer has argued that the temperature of the 
Sun ought to decrease by radiation to the extent 
of 3J° annually. 

But these assumptions are all based on the 
supposition that the heat received on our globe 
is equal to the amount received in space at the 
same distance from the Sun ; whereas we know 
that the amount of the sensation of heat de- 
pends upon the medium through which it acts. 
The Sun's rays always warm us the most power- 
fully when the atmosphere is most dense ; and 
this is evident, not only from an appeal to the 
senses, but from a consideration of the character 
of light. The more dense the air, the greater is 
the number of air particles which are set in mo- 
tion in a given space, by the pulsations of the 
light-wave. Hence it is that snow is never 
absent from the tops of high mountains, even 
under the zenith Sun of the equatorial regions, 
though nearer to the Sun than the luxuriant val- 
leys at their bases. A series of balloon ascen- 



CAUSE OF HEAT. 43 

sions, made some time ago in England, showed 
that up to the height of one mile the temperature 
decreased much more rapidly than the baromet- 
ric pressure ; which fact is doubtless attributable 
to radiation of heat from the surface. But above 
the height of one mile the temperature decreases 
steadily in the exact ratio of the air's density, 
which is known to decrease with an augmenta- 
tion in the altitude. We are warranted in con- 
cluding that where there is no matter there is no 
heat. It is an established fact that heat is the 
result of the vibration of material particles, and 
where there are no particles to be vibrated there 
can be no manifestation of heat. Hence the tem- 
perature of the interplanetary spaces must be 
very nearly that of absolute cold, because they 
contain but very little diffused matter. "We can 
demonstrate that outside of the cometary masses, 
the serolitic particles, and the planetary bodies, 
with their atmospheres, the whole globe bounded 
by the orbit of Neptune, does not contain so 
much matter as would weigh a single grain. 

There is only one way in which we can hope 
to measure the temperature of the Sun ; the way 
was first pointed out by me in June, 1870, but it 
is far from giving precise results, as yet, owing 
to our want of knowledge of the absolute zero of 
heat. The zero of our present thermometric 
scale is entirely arbitrary, being about one-sixth 
as far below the freezing point of water, as the 



44 ZERO OF HEAT. 

distance from the freezing to the boiling point. 
Sir John Herschel estimated the temperature of 
the planetary spaces to be not less than 260° 
below the freezing point, and Pouillet places it 
256° below, while some recent experiments on 
the gases indicate about 460° below the freezing 
of water, as the point at which they lose their 
elasticity. Assuming 260° as the true quantity, 
and that the Earth's average surface temperature 
would be 40° below the freezing point but for 
the warming influences of the Sun, we have the 
difference of 220° of the Fahrenheit scale, as the 
heat of the Earth's surface above absolute zero ; 
independent of the average of 66° received from 
the Sun to bring her average temperature up to 
58° of the thermometer. 

Now : what is it that causes the Earth's inde- 
pendent surface temperature to stand 220° higher 
than that of the interplanetary spaces ? We have 
already seen that the temperature of the air varies 
with its density, and the same is true of the Earth. 
The sensation of heat is due to the mutual pres- 
sure of contiguous atoms. Hence, when those 
atoms are widely sundered, there is but little 
heat ; when they are forced together more closely, 
the sensation of heat is produced, — as may easily 
be proven by compressing any given quantity of 
air into a less space than it formerly occupied. 
We have good reason to know that all matter is 
in a state of continuous vibration, like the motes 



CHANGE OF FORM. 45 

which we can all see dancing in the sunbeam, 
even in a still atmosphere. When we increase 
the heat of a body we do it by increasing the 
tendency of its constituent atoms to move ; or, in 
other words, by causing them to enlarge their 
arcs of vibration. This increases the pressure of 
the atoms upon each other, and this, again, results 
in the well-known augmentation of bulk which 
accompanies an increase of temperature, causing 
liquids to boil over, and the mercury to rise in 
the tube of the thermometer. All matter increases 
in bulk as it becomes warmer ; and we can always 
measure the amount of heat by measuring the 
bulk of the warmed or cooled body, and compar- 
ing it with the bulk at a known temperature, 
though all bodies do not expand equally with 
equal additions of heat. Solid bodies expand as 
the temperature rises, till they reach a point 
where the repelling power becomes greater than 
the force which binds the atoms together in solid 
form, and they become fluid; water takes up 
140° of heat in passing from the solid to the 
liquid form. Liquids, too, expand with aug- 
mentation of temperature, till the mutual repul- 
sion of their atoms becomes so great as to 
overcome the attraction of the liquid form, and 
then the body becomes a gas or vapor. One 
cubic inch of water expands into one cubic 
foot of steam, and takes up 972° of heat in 
making the change ; the constituent atoms are 



46 MEASURE OF EARTH 

driven so much, farther apart that their arcs of 
vibration can be increased by the amount repre- 
sented by 972° of heat excitement, before the 
particles of the steam press as forcibly upon each 
other as did the particles of boiling water. We 
find that heat is the repulsive force which keeps 
asunder the atoms of matter, as attraction is the 
force that draws them together. Between the 
two, the ever-changing, yet ever-constant, equi- 
librium of nature is preserved. The force with 
which the constituent atoms of a mass of matter 
press upon each other, measures the amount of 
heat felt. Where there is no matter, there can 
be no atomic pressure — hence no heat. 

The pressure of Earth atoms upon each other 
gives a certain amount of sensible heat at the 
Earth's surface, independently of the vibrations 
caused by solar action ; and because the pressure 
is increased as we descend below the surface, 
being equal to the weight of the particles at any 
point, added to the weight of the superincumbent 
matter, therefore the heat increases as we des- 
cend; the augmentation averaging about 1° for 
every 75 feet in depth. It is estimated that the 
Earth's surface is warmed 40 times as much by 
the Sun as by radiation of heat from her interior. 
In like manner the pressure of the Solar atoms 
upon each other is a measure of the amount of 
Sun heat. Let us compare the two : 

We saw in the second lecture of this course 



AND SUN HEAT. 47 

that the force of attraction at the Sun's surface 
is about 27 times that at the surface of the 
Earth ; the Sun's particles being drawn together 
by the force of their mutual attraction 27 times 
more forcibly than those of the Earth. But we 
also saw that the density of the Sun is only one- 
quarter that of the Earth ; the particles of the 
Sun are kept four times as far asunder, though 
pulled together with 27 times greater force than 
those of the Earth. The only possible explana- 
tion of this is that the repulsive force is 4 x 27, 
or 108, times greater on the Sun's surface than 
on the Earth ; which is as much as to say that 
the Sun is 108 times hotter than the Earth. But 
108 times 220 equals 23,760°, which should, 
therefore, be the heat at the Sun's surface, as 
measured from the absolute zero; or 23.500° 
above the freezing point of water. Like the 
Earth, the temperature of the Sun must increase, 
under greater pressure, with an approach toward 
his centre. The temperature of 23.500° is that 
at the point corresponding to the place where the 
air and water meet on the Earth. 

At such temperatures as these it would seem 
impossible that matter could retain the solid 
condition, even for a moment ; and indeed, we 
see that iron, and magnesium, sodium, and other 
metals, are reduced to a state of vapor in the 
Sun's chromosphere. But the spectroscope shows 
that they also exist in the liquid form nearer the 



48 



centre, that condition being undoubtedly main- 
tained by the greater pressure of the exterior 
matter. It is, perhaps, also possible that, near 
the centre, the still greater pressure may be great 
enough to form a solid nucleus for the Sun, not- 
withstanding the vastly augmented heat ; as some 
of our gases can be compressed into the solid 
form. Of this we can know nothing; but we 
are enabled to judge that the Sun is, relatively 
speaking, a mass of fluid matter, only about one- 
fourth the weight of an equal bulk of earth, and 
lacking the solid crust which gives stability to 
the surface of our globe, and renders possible 
vegetable and animal existences, such as those by 
which we are surrounded. If there be any solid 
form of matter at any considerable distance from 
the Sun's centre, it is, in all probability, to be 
met with temporarily only, and near the outer 
limits of the solar atmosphere. Huge cakes, or 
flakes, of solid matter may be formed there, 
where the temperature is sufficiently low to permit 
it, just as ice is formed on the surface of a sheet 
of water ; but the strong upward and downward 
currents, which we have yet to note at greater 
length, perpetually carry these flakes downward 
to be melted into liquidity by the greater heat ; 
and their place is taken by cooler matter, to be, 
in its turn, solidified and carried down deep into 
the molten sea. 

We have also reason to believe that the chem- 



CONSTITUTION. 49 

ical elements existing in the Sun are not com- 
bined so intricately, or so numerously, as on our 
Earth. Here we very seldom obtain a pure ele- 
ment, except by artificial means, and then it is 
difficult to keep it pure. In the atmosphere we 
have .a mixture of two principal gases — oxygen 
and nitrogen — but these are always found to be 
mixed with hydrogen and carbon ; and, in addi- 
tion to these, the atmosphere contains small por- 
tions of other forms of matter, either simple or 
compound. Pure water is a compound of oxy- 
gen and hydrogen, but we can seldom obtain it 
unmixed with other elements. So our rocks and 
earths are compounds ; and even the metals have 
to be separated from baser dross, with which 
they are found associated, in the ore taken from 
the mine. 

We know that on this Earth, up to a certain 
point, the elements combine most readily at high 
temperatures. But, far below the point of Sun 
heat this limit is passed, and the tendency of the 
different substances is to separate into distinct 
aggregations ; and this appears to be the case in 
the Sun. 

At the time of a total eclipse of the Sun, when 
the interposition of the Moon's dark body shuts 
off his light, large rosy-colored masses are seen 
projecting out beyond the edge of the Moon, 
which not infrequently attain an altitude of 50,- 
000 miles or more above the Sun's normal sur- 
3 



50 NO COMBUSTION 

face. It has very recently been found possible 
to study these interesting objects in the absence 
of an eclipse. When the spectroscope is directed 
to the exterior portion of a protuberance, the 
only lines seen in the spectrum are those which 
indicate the presence of hydrogen; this shows 
that immense volumes of that gas exist as a dis- 
tinct form, unmixed with other matter. Directed 
lower down, the instrument usually shows simi- 
lar, but smaller, aggregations of sodium, magne- 
sium, and iron. And these substances are not 
blended, as two gases will mix on our Earth, 
but exist separately, as oil and water will do 
when poured into the same vessel. The lighter 
gases appear to take the exterior place, just as 
they would do with us were it not for their ten- 
dency to unite chemically or mechanically when- " 
ever brought into contact. 

These facts tend to prove that the Sun's ability 
to supply light and heat are not kept up by com- 
bustion, which involves a chemical union of pre- 
viously separated elements. When we burn 
substances, we set in motion a very simple 
chemical process, in which the oxygen of the 
atmosphere unites with the hydrogen, or the 
carbon, of the burning body, and forms water, 
or carbonic acid; and this, if collected, and 
weighed along with the ashes, will be found to 
give a total exactly equal to the weight of the 
substance before it was burned, added to the 



IN THE SUN. 51 

weight of the oxygen taken from the air. And 
these results of combustion are unburnable. If 
the Sun were a burning body it would be neces- 
sary to get rid of tremendous quantities of water 
every minute in order to prevent the water from 
quenching the fire ; and if the process could have 
been kept pp, in spite of this difficulty, for the 
past 5,000 years, the Sun would by this time 
have been reduced to a mass of water, or a mere 
cinder, with nothing left to burn. But we have 
no evidence of the presence of water in the Sun, 
nor even of a single atom of oxygen, without 
w T hich combustion can not be carried on. The 
only chemical combinations which appear to be 
possible are those on the Sun's exterior, beyond 
the limits of the luminous atmosphere ; and the 
vibrations there excited are very probably the 
causes of many of the chemical activities which 
are produced on this Earth by the non-luminous 
portions of the solar ray. 

It has recently been argued that the Sun's light 
and heat are kept up by the fall of meteoric 
matter toward him. It is well known that heat 
and motion are convertible into each other — 
that the sudden arrestation of motion produces 
heat, as shown in the ignition of meteorites by 
coming in contact with the Earth's atmosphere 
at the rate of about 30 miles per second. The 
exact equation of the two has been calculated ; 
and it is found that a rise in the temperature of 



52 CAUSES OF SOLAR 

a pound of water, to the extent of 1°, is equal to 
the lifting of that pound of water through a height 
of 772 feet. It has also been calculated that, in 
the case of bodies falling into the Sun, the rate 
of movement just before the collision can not be 
less than 277, nor more than about 392, miles per 
second. Mayer computes from this that the fall 
of an asteroid into the Sun produces from 4600 to 
9200 times as much heat as would be generated 
by the combustion of an equal mass of coal, and 
estimates that the aggregate of matter falling 
into the Sun every minute is equal to not less 
than 21,725, nor more than 43,550, cubic miles of 
water. According to this theory Mr. Thompson 
has calculated that the falling of the Earth into 
the Sun would generate heat enough to cover 'the 
expenditure of 95 years, and all the primary 
planets of the system would maintain it for only 
about 45,600 years. I have recently calculated 
that the quantity of matter coursing around the 
Sun, in the shape of comets, planetoids, meteor- 
ites, etc., is from one and a quarter to one and a 
half times as much as the aggregated masses of 
all the planetary bodies, including the Earth ; 
and this would give a supply for about 65,000 
years additional. Even with this addition, the 
Sun, as such, could not exist more than 110,000 
years from the present time. But we have good 
reason to believe that the Earth has been warmed 
and lighted by the sun for a longer period than 



LIGHT AND HEAT. 53 

this, without any planetary accretion whatever. 
The theory is, therefore, untenable, and scientific 
men are generally abandoning it. 

The only theory which seems to be compatible 
with the observed facts is that which assumes the 
solar phenomena of light and heat to be pro- 
duced by the rapid and intense vibration of the 
Sun's matter, due to the great heat, which is, 
itself, principally caused by the tremendous pres- 
sure of the constituent atoms, resulting from the 
attraction of gravitation. The loss of this heat 
by radiation is necessarily followed, and par- 
tially compensated, by a continuous condensation 
of the solar mass, which would be appreciable at 
this distance, only after the lapse of thousands of 
millions of years. The telescope shows us that 
the Sun is the theatre of incessant movements, 
to the rapidity of which our Earth furnishes no 
parallel. The spots, which have been unusually 
numerous during 1870, are evidences of storms 
in the Sun's atmosphere, which are undoubtedly 
accompanied by tremendous convulsions in the 
interior mass. These spots, many of which are 
more than a million square miles in area, are 
shown to be depressions in the Sun's surface, 
almost funnel shaped, and are evidences of a 
downward rush of 'molten matter, similar to that 
which marks the whirlpools produced by two 
opposing currents of water ; but on so much 
grander a scale that the comparison fails to con- 



54: TEACHINGS OF 

vey even a faint idea of the phenomenon. The 
protuberances seen during a total eclipse of the 
Sun, and which appear at other times as brilliant 
protrusions, called faculae, almost always visible 
in the neighborhood of the spots, are the swelling 
upward of the throbbing mass beneath, which 
would be paralleled on our Earth if a hundred 
volcanoes should vomit forth their liquid lava, 
all at the one time, and the accompanying con- 
vulsions of the interior fluid mass were unre- 
strained by the solid crust surrounding it. These 
spots and faculae sometimes change their positions 
on the Sun's surface at the rate of 100 miles per 
second, and their forms change with equal celer- 
ity ; spots having an area of many thousands of 
square miles, have been observed to form, and 
entirely disappear, within the space of a few 
hours. These mighty movements in the solar 
mass are cause enough for the vibrations needed 
to light and warm a million worlds like ours. 

These are some of the lessons which are gath- 
ered by patient study of a single sunbeam. The 
ancient world, though not able to comprehend 
the value of light as a teacher of science, was yet 
wise enough to recognize it as a most potent 
instructor ; and one of the most deep-lying fund- 
amentals of the structure of human language is 
that which assimilates light to knowledge. Grop- 
ing along blindly in the darkness of ignorance of 
nature's laws, the philosophers of olden times 



THE SUNBEAM. 55 

sighed for a flood of light to illume their path- 
way. We have attained that which u All their 
wise men waited for; and sought, but never 
found." 

Strangely enough ; modern science has illu- 
minated the pathway of man into these arcana 
in a way directly opposed to ancient conceptions. 
Our predecessors prayed for more light ; we 
found toomueh of it, for the purposes of study ; 
and the grandest step in the investigation was 
taken when we had puzzled out the waj r in which 
we could slice it up into almost infinitessimal 
portions, and study in detail the dissected com- 
ponents of a single beam. 

And it is thus with all knowledge. The 
human mind is so constituted that it can lay 
hold of but little at a time, though it can grasp 
immensity itself when taken in by little and little, 
while the mind grows with what it feeds on. 
Facts must be mastered in minute detail if the 
truth be attainable by finite minds. The knowl- 
edge of the infinite, like the light of the Sun, is 
too dazzling for the eyes of mortals ; but the 
right acceptation of a simple revealed truth may 
help us onward in our path toward immortality ; 
as we can reach out to a comprehension of the 
glory of the meridian Sun by grappling with a 
minute portion of his beams, and find in that 
knowledge a key to the conditions of other, and 
far more distant, worlds. 



BIOLOGY OF THE UOTYEESE. 



Habitability of other Worlds. Life on the Earth : Con- 
ditions of Organized Existence; Limitations of Tem- 
perature. Sun and Stars, too hot; Moon too cold — 
died out. Earth once like the Sun is to-day. Life on 
the Planets; Maps of Mars; the Planetoids. Invisible 
Worlds, Light, Heat, and Electricity; all Different 
Expressions of one Force. The Sun's Light and Heat 
variable; his Spots; their Influences on other Bodies ; 
Earth weather of 1870. Variable Stars; Changes in 
Color and Brightness; Causes and Effects. Greater 
Cycles of Change. History of the Universe; Growth, 
Maturity, and Decay of Worlds, Systems, and the Uni- 
verse. Diversity of Atoms. Future of the Cosmos. 



One of the most interesting of all the questions 
which are suggested by a contemplation of As- 
tronomical facts is: Are the Sun, Stars, and 
Planets inhabited ? and, if so, are they, or any of 
them, inhabited by beings like ourselves, capable 
of reasoning out the leading facts in the condi- 
tions of the Universe? 

The question has often been asked, and often 
answered ; but the response was not always an 
intelligent one, though generally in the affirma- 
tive. "We examine the Earth, and find that it is 
full of vitality — swarming with life 3 under all 



LIFE ON THE EARTH. 57 

the conditions which seem to us possible. The 
surface is literally covered with animal and 
vegetable existences; and every one of those 
individuals, is, itself, the seat of divided life ; 
parasites innumerable live on its exterior, and 
countless millions of minute creatures exist in the 
interior, even of the healthiest human being. 
The waters of the ocean and river teem with life ; 
and even the solid rock is in large part made up 
of the remains of animal and plant life, which 
enable us to trace out the history of our planet 
millions of ages ago. It would seem to have 
been the design of the Creator to multiply the 
individualities of existence on this earth, to the 
greatest possible extent — to cause the phenom- 
ena of life wherever they could be sustained, and 
to make of our world one vast theatre of vitality, 
in which every unit of living organism should 
not only enjoy life itself, but be the means of 
sustaining the lives of other beings. It has been 
argued that it is simply absurd to suppose that so 
much creative ability should have been exerted 
on our planet, while other and larger worlds were 
left unpeopled. 

The argument from analogy is a very powerful 
one, when rightly applied ; in fact it is the grand 
tool with which we work out truths in Nature — 
new to us, though older than the hills, which 
have been called eternal. But the argument is 
valueless, if loosely conducted. If we first study 



58 life limits: 

out the conditions under which life is met with 
on our Earth, and find that those conditions exist 
in other bodies, we are warranted in assuming 
that organized beings exist in other worlds than 
ours. If, on the other hand, we find conditions 
in some other worlds which do not admit of the 
possibility of life, as we understand it, then we 
are warranted in stating the fact ; though we can 
not say that there are no variations of material 
animation possible outside the limits of our 
sphere of observation. Of course we can only 
deal with material life. The domain of spirit 
existence is beyond our ken, and has nothing to 
do with the inquiry ; since, in the case of spirit 
life, as distinct from material organization, there 
is no bond that connects it with this or that 
aggregation of matter which we call a planet or 
a star. "We can not believe in spirits which are 
more intimately identified with Jupiter than with 
the Earth, unless as they may have been con- 
nected in the past with material organizations on, 
or in, one of those bodies. 

We find that life is possible on our globe, under 
a wide range of conditions — in earth, air, water; 
as an independent organization, or growing 
and subsisting directly on some other animal or 
vegetable structure ; or in animalcular form, 
inhabiting the globule of water, or the single 
drop of blood, in uncounted millions. There is 
only one mode in which material life can be 



TEMPERATURE. 59 

gauged universally ; that is by the fact of organ- 
ization ; there is only one way in which the pos- 
sibilities of organization can be limited : — by 
temperature. And we find that almost every 
class of animal and vegetable life has its own 
very narrow limits of temperature, ranging over 
but a very few degrees of the scale, while all are 
possible only within a few score degrees of tem- 
perature. Hence it is that most animals and 
plants are met with only within narrow belts of 
longitude; the reindeer and seal of the polar 
regions could not change places with the tiger 
and alligator of tropical climes ; the grape requires 
a warmer climate than the apple ; barley will 
grow where it is too cold for wheat culture ; and 
wheat is grown successfully in climates where 
the solar rays are not strong enough to mature a 
single ear of corn. It seems as if every separate 
organization recognizes one particular degree of 
heat as that which is most congenial to the devel- 
opment of its structure ; just as it appears prob- 
able that the properties of the several chemical 
elements are also determined by the different 
capacities for specific heat, which have been 
impressed upon their atoms. 

The domain of animal and vegetable life, as 
ordinarily understood, has a range of only about 
90° of temperature, or from 30° to 120° of the 
Fahrenheit scale. At 32° water (a large com- 
ponent of organized fluids) congeals, rendering 



60 LIMITATIONS OF 

impossible the circulation of blood in tlie animal, 
and of sap in the vegetable ; while above 
120° the chemical affinities are so active as to 
forbid permanence of form. The animal world 
is provided with apparatus for keeping its tem- 
perature nearly equable, at an average of about 
half way along this scale. Man and the warm- 
blooded animals keep in the upper half of the 
scale by dint of burning large quantities of car- 
bon within the body, the carbon being taken up 
as food, and the required oxygen being taken in 
through the lungs. And the amount of heat thus 
evolved measures the muscular power of the ani- 
mal, as of the steam engine. The total muscular 
force exerted through the life-time of an ordinary 
man is about equal to the force which is obtained 
by burning three tons of coal. 

The same process of heat-making goes on, but 
much more slowly, in the colder-bodied fishes 
and reptiles. Hence the necessity for an atmos- 
phere — either of air, or water, or both ; and 
this is also necessary to give force to the solar 
ray, as explained in the preceding lecture. With- 
out an atmosphere, the Sun's rays would not 
warm the surface of our globe sufficiently to keep 
up the temperature required to support life ; even 
if it were not necessary to respiration. 

All life is not impossible outside of these nar- 
row limits of temperature ; but the range is yet 
small, within which living organisms can exist. 



ORGANIZED EXISTENCE. 61 

We may lay it clown as a rule that the higher 
the form of vitality the more complex is the 
accompanying organism, and the less the ability 
to depart from the normal standard of tempera- 
ture. It is true that man can endure great ex- 
tremes of heat and cold ; but this is accomplished 
only because, artificially or otherwise, he is able 
to preserve the healthful temperature under 
adverse conditions. You can not change the 
temperature of the human body 2° either way 
without causing violent sickness ; nor 10° with- 
out producing death. But some of the lower 
orders of organized existence have been imbed- 
ded in ice, and others immersed in water nearly 
at the boiling point, without losing their vitality. 
The w r hole range under which any form of organ- 
ized existence is possible, may be safely estimated 
to lie within 300° of the Fahrenheit scale; between 
100° below and 200° above, the freezing point. 

The temperatures at the surfaces of the Sun 
and fixed stars are far above these limits — can 
be measured only in thousands of degrees of 
heat, instead of hundreds. And the heat is so 
great as to prevent the matter of which they are 
composed from retaining the solid form. Hence 
there is no more of fixity on the surface of a self- 
luminous star than in mid-ocean ; and the idea 
of special locality is absent. We conclude, there- 
fore, that the Sun and fixed stars are not habita- 
ble globes themselves ; but that their office is to 



62 the moon: 

furnish the light and heat necessary to make 
other globes habitable. They are like the Shak- 
sperian hero ; who, though not witty himself, 
was the cause of wit in others. The analogy 
does justify us in concluding that the numberless 
fixed stars which dot the firmament were not 
created in vain, and that they are, therefore, like 
our own Sun, the centres of vitalizing power, each 
to many worlds, though so far removed from 
us that we see them not ; the light of the stars, 
reflected from their surfaces, is too feeble to reach 
our eyes at such immense distances. 

How is it with our nearest neighbor, the Moon ? 
In the first place, she has no atmosphere. We 
never see any clouds in the Moon, even with the 
most powerful telescope ; the same dull, unvary- 
ing appearance is always presented to us, except 
as her change of position with regard to the Sun 
enables us to see more or less of that side which 
is always turned towards us. The Moon has very 
often been seen to pass, apparently, over a star, 
hiding it from view for about an hour. If the 
Moon had an atmosphere, the star would appear 
and disappear gradually, being comparatively 
dull when seen through the aerial envelope of 
the Moon, just before, and just after, the appa- 
rent contact with the solid bulk of our satellite. 
But the appearance and disappearance are instan- 
taneous. This fact also proves that there is no 
water on the Moon's surface ; because water will 



A SCENE OF DESOLATION. 63 

always vaporize, even at the lowest temperatures, 
if the pressure of the atmosphere be removed. 
Place a basin of water, or even a lump of ice, 
under the receiver of an air pump, and exhaust 
the air. The glass will be immediately filled by 
a cloud of vapor rising from the water or the ice. 
If there ^yere any water on the Moon it would 
form an atmosphere ; of which there is no trace. 
The Moon has no aerial envelope, and therefore 
no breathing animal can exist on her surface ; 
nor can the ray of sunlight produce warmth 
enough to support the existence of any vital 
organism. There is no life, no cloud, no wind, 
no water, no refraction of light, on the Moon. 
Her surface is a barren desert, from which both 
Sun and stars could be seen at the same time 
against the black background of the sky, could 
any being view the scene from such a situation. 
But it w r as not always thus with the Moon. 
She was not ever the barren waste we see her 
now. Her surface is diversified by bright promi- 
nences, which are known to be mountain peaks 
and ranges, and hill country ; broken up by vol- 
canoes, all of which are believed to be now ex- 
tinct. These mountains are much higher, propor- 
tionately, than any on our globe ; some of them 
being 24,000 to 27,000 feet high. Not less than 
39 peaks have been measured, the height of each 
of which exceeds that of Mont Blanc. Between 
these mountains are dark patches, that were 



64: the moon: 

formerly thought to be oceans, bat the large 
telescopes recently come into use show them to 
be nothing but old sea bottoms. They were 
once filled with water, and the Lunar surface 
was once diversified by land and ocean, lofty 
mountain scenery, and fruitful valleys, as the 
Earth is now ; and was surrounded by an atmos- 
phere which permitted the existence of beings 
similar to those found on this Earth. But the 
water has vanished, and the atmosphere has 
departed, making the Moon a vast burying- 
ground, on which repose, in undisturbed still- 
ness, the debris of untold generations of animal 
and vegetable life. 

In the Sun, Earth, and Moon, we have three 
remarkably distinct sets of conditions, which it 
will be instructive to compare. The Moon has 
once been habitable like our Earth; has the 
Earth ever been an incandescent mass, like the 
Sun? and will both Sun and Earth ever be 
reduced to the present condition of the Moon ? 

To the first question we can answer "Yes;" 
to the second — " very probably." 

The Earth becomes warmer, at the rate of 
about 1° for every 75 feet, as we descend below 
the surface ; and fully 300 volcanoes, on different 
parts of the Earth's surface, vomit up red-hot 
liquid matter from her interior in the present 
century — two of the most active of which are 
situated in the polar regions. We refer to 



ONCE INHABITED. 65 

Mount Hecla in Iceland ; and Mount Erebus, 
near the South Pole. We have every reason to 
believe that the Earth's solid portion is but about 
16 miles in thickness, and that all within this 
is a densely fluid mass, 6 or 7 times heavier than 
an equal bulk of water, in an intensely heated 
condition, analogous to the state of the Sun. The 
present crust of the Earth has been made by the 
process of cooling, through a period of not less 
than 100,000,000 of years, previous to which it 
was undoubtedly a mass of incandescent matter, 
and emitted light and heat as the Sun does now. 
That the whole globe was once fluid is proven 
by the fact that the Earth's polar diameter is 26-J 
miles shorter than the Equatorial diameter — a 
fact which can be accounted for in no other way 
than on the supposition that she then rotated on 
her axis, as now ; and that the attraction of the 
matter in the equatorial regions, being partially 
overcome by the velocity of rotation, the yielding 
mass accumulated toward the Equator, causing 
the bulging shape which is shown by the meas- 
urements spoken of in the first lecture of this 
series. Take a ball of dough, and thrust a stick 
through the middle, then turn it around rapidly ; 
it will be found to assume the flattened shape 
noticed in the case of the Earth. If, however, 
the dough be stiffened, by baking, the change 
in shape is no longer possible. The Earth could 
not have become flattened at the poles unless 



66 the eaeth's history: 

once fluid; nor after the formation of a thick 
crust by cooling. 

The former incandescent fluidity of the whole 
Earth is more directly shown by an examination 
of its cooled crust. We find it to consist of a 
number of distinct layers, which, although some- 
what mixed in many places by subsequent up- 
heavals of the molten mass beneath, yet occur 
with sufficient regularity to permit us to ascer- 
tain the exact order of their formation, though 
we may not be acquainted with the first in the 
series. "We find that the lowest of the known 
rocks, the granitic, are of fiery origin; though 
some of them have been thought to show signs 
of stratification. They are composed of nearly 
one-half oxygen, and the other half a fused min- 
eral. The rocks above the granitic have evi- 
dently been formed from it, and each other, by 
the action of water; and have been deposited, 
one above the other, in layers, which contain the 
remains of animal life, showing that some forms 
of organized vitality have existed on the Earth 
ever since the first formation of a granitic crust, 
of perhaps not more than half a mile in thick- 
ness. And not only the individuals, but the 
types of these existences, have been many times 
changed in the past, to correspond with the 
altering conditions of the surface. 

The Earth is still cooling ; but the process is 
less and less rapid as the increasing thickness of 



HER FUTURE. 67 

the crust augments the resistance which it offers 
to the escape of the internal heat. Bischoff esti- 
mates the present rate of cooling to be about 1^-° 
in a million years, and that the internal heat 
adds only -fa of a degree to the temperature of 
the surface. As it cools, the interior mass is 
continually shrinking in bulk, leaving an inter- 
val between it and the crust. If the outer shell 
were of uniform weight and consistency, its sta- 
bility would be but little affected by the shrink- 
ing. But it consists of substances unequally 
cohesive, and gives way in the weakest part, 
when the whole crust closes in around the central 
mass. These collapses would be frequent in the 
early days of our geologic history ; they occur 
now at longer intervals, as the crust becomes 
stronger with increasing thickness. We have 
evidences that several such collapses have oc- 
curred in the past. But a time at length arrives 
when the crust is so thick that it is strong enough 
to bear the strain of its own weight. The crust 
will also continue to cool as the internal heat 
diminishes, and will crack open with the resulting 
contraction in its bulk, forming huge fissures 
above, and vast caverns beneath, into which the 
waters of the ocean will rush, and thence be 
absorbed by the chilled strata, losing themselves 
for ever out of the reach of the evaporating forces 
now at work on the surface. It is estimated that 
our Earth's crust has already absorbed one-fiftieth 



68 CAUSES OF 

part of her original ocean, and that every drop 
will have disappeared by the time the crust has 
attained a thickness of one hundred miles. The 
Earth could absorb 50 times as much water as 
now exists on her surface, if cooled down to a 
sufficiently low point. When the water disap- 
pears, the phenomena of evaporation and rainfall, 
which now keep up the circle of life sustenance 
here, will vanish also. The cold atmosphere 
will lose its vapor of water, as the capacity of 
the air for taking up vapor diminishes rapidly 
with decrease of temperature; and the atmos- 
phere itself will at length disappear, its compon- 
ent gases becoming too cold to preserve their 
elasticity. Long before this every living thing 
will have died out from our globe, and its surface 
will be left as barren and as inert as that of the 
Moon is to-day. 

It is now very well understood that the capac- 
ity of the Earth to sustain organized creatures is 
being rapidly diminished in another way. Car- 
bon, as one of the four organic elements, is essen- 
tial to their existence, and they are continually 
engaged in eliminating it from the air and from 
water, one important product being the carbon- 
ates of lime (as chalk), which form a large pro- 
portion of the bony structure of animals. This 
compound is resolved with difficulty, and it is 
now a well-established fact that the deposits of 
carbonate of lime are rapidly increasing, espe- 



DYING OUT. 69 

cially at the bottom of the sea, where they lie 
undisturbed by the action of the waves above. 
The atmosphere is thus losing its carbon, and 
therefore losing its ability to supply the material 
from which are built up the bony tissues of the 
animal economy. Long before the atmosphere 
is absorbed by the Earth's crust it will have lost 
all its carbon, and lose with it the capacity to 
supply the skeleton which is the physical founda- 
tion of animal life. 

We have telescopic evidence that the Moon 
has passed through the changes above noted. 
As many as 425 lines have been counted on her 
surface, which are called rilles, and are undoubt- 
edly cracks, of the character referred to, through 
which the waters and the atmosphere have dis- 
appeared. The Moon has passed through these 
destructive phases much sooner than the Earth, 
because she is so much smaller a body, and pre- 
sents a much larger radiating surface in propor- 
tion to the volume of matter to be cooled. The 
Earth's diameter is (3.666) 3f times larger than 
that of the Moon ; her surface is 13-J- times greater, 
and her volume is 49 times greater. Hence, the 
Moon's radiating surface is, proportionately, 
nearly four times greater than that of the Earth. 

In this difference of mass we have, also, the 
cause of the slow rotation of the Moon on her 
axis — only one rotation being performed in a 
little less than a month. The attraction of the 



70 LOSS OF AXIAL MOTION. 

Moon causes a heaping up of the waters of our 
ocean, to the height of about four feet in the open 
sea, forming the tides, which follow the Moon in 
her apparent diurnal passage around the Earth 
from East to West. This being in a direction 
contrary to that in which the Earth is turning, 
the result of the friction of the waters is to retard 
the Earth's time of diurnal rotation, at the rate 
of about 1 second in 4^- centuries. When the 
Moon had an ocean the Earth caused correspond- 
ing tides on her surface, but nearly 85 times 
greater, the Earth being so much heavier than 
the Moon, and the retarding force was corre- 
spondingly increased. The force of rotation on 
the axis, relative to the Earth, was destroyed by 
the friction, before the waters left her surface; 
and the effect of the Moon's attraction on our 
ocean will be to destroy the Earth's axial rota- 
tion in precisely the same way. The time required 
to work this stupendous change is estimated to 
be about 26 millions of years. This retardation 
of the Earth's axial motion, combined with an 
actual acceleration of the Moon's movement in 
her orbit, gives rise to an apparent quickening of 
the Moon's rate of movement round us, as meas- 
ured in Earth days, to the extent of about 12 
seconds in a century. It is necessary to make 
this allowance in order that the calculation of 
former Eclipses shall agree with the recorded 
observations of the times when they occurred. 



THE SUN COOLING OFF. 71 

For the same reasons as those we have given, 
the Sun has not cooled off so rapidly as the 
Earth, when at the same actual temperature, 
though he is losing heat more rapidly than the 
Earth is now. His volume is 1,250,000 times 
that of the Earth, while his surface is only 11,634 
times greater. Taking the estimate of Professor 
Mayer, that the Sun's surface cools now at the 
rate of 3J° annually, he would still give out light 
and heat enough to maintain life on our globe for 
60,000 years to come ; and it is probable that this 
estimate of time is much too small. I have cal- 
culated that the Sun would lose one-quarter of 
his present lighting and heating force in about 
one hundred thousand years, by radiation ; if 
there were no compensation by compression, or 
the fall of planetoid al matter to his surface. We 
can scarcely suppose it possible that the Sun 
should be lighted and heated by some far-distant 
body, sufficiently to make life possible on his 
surface after his own light has gone out forever. 
The Sun was never inhabited; and probably 
never will be, otherwise than by beings who can 
exist without light. He is still fluid, but, unlike 
our globe, he presents no evidence of flattening 
at the poles. The reason is that his velocity of 
rotation is relatively small. He occupies 25-J 
days in turning once round on his axis. The 
rotation of the Sun lessens the weight of bodies 
at his equator by only one part in about 18,000. 



72 THE PLANET JUPITER : 

At the Earth's equator the loss of weight is more 
than one part in 300. 

When we examine the light of the planet Ju- 
piter we find that it is reflected light, but so 
intense in proportion to the area of reflecting 
surface, and the distance from us, as to lead us 
to conclude that he reflects all the sunlight 
received by him, which he could not do unless 
his atmosphere were very dense — almost imper- 
vious to the passage of the light ray. Looking 
at him through the telescope, we see his apparent 
disc crossed by broad bands of dusky hue, which 
cross a brighter background, in directions nearly 
parallel to the equator of the planet. These belts 
vary their form and position, showing that they 
do not form a part of the solid planet, like the 
unvarying irregularities of the lunar surface, but 
that they are phenomena of his atmosphere, like 
the spots in the Sun. If we compare them with 
the currents in the atmosphere of our Earth, we 
find a striking similarity of position and change. 
On our globe we have the trade winds blowing 
from the East, on each side of a calm-belt, which 
shifts back and forth across the equator, with the 
changing declination of the San. Outside of 
these we have a calm-belt in each hemisphere, 
and further towards the poles another belt of 
winds, called the anti-trades, which blow from 
the west. "We see also spots among his belts, 
analogous to the Sun spots. We conclude that 



NOT YET HABITABLE. 73 

we do not see the planet at all, but only his 
atmosphere, which* is agitated in a similar man- 
ner to that of the Earth, but is of much greater 
density, hanging around the planet like a heavy 
cloud, and containing in suspension all the water 
which will form the future oceans of Jupiter. 
The planet is some 1300 times larger than the 
Earth ; but, if the disc we see be that of the solid 
body, its density is but (0.22) a little more than 
one-fifth that of the Earth — scarcely so great as 
that of the Sun. Either Jupiter is as yet uncon- 
densed into the solid form, or his crust is not 
sufficiently cooled to permit the deposition of 
water on his surface from the vapor clouds in 
his atmosphere. In either case he is not yet fit 
for the habitation of living beings ; and this accords 
with the analogy that, being so much larger than 
the Earth, he should be much longer 'in cooling, 
while he should have cooled more rapidly than 
the Sun, as being less in size than the central 
luminary. Jupiter was a self-luminous body, a 
sun to his four moons, not many thousands of 
years ago ; he will be a habitable globe, like 
our Earth, many thousands of years hence. His 
satellites are probably habitable to-day. All but 
the second are larger than our Moon, and the 
diameter of the third is nearly one-half that of 
the Earth. The spots seen on the surface of 
Jupiter show that the vast orb of 85,390 miles in 
diameter rotates on his own axis once in a little 
4 



74 SATUKN. 

less than 10 hours. This great velocity causes a 
corresponding flattening at the poles, of ^ while 
that of the Earth is only a little more than -gfo. 

Saturn is ninety times as large as the Earth, 
and his density is only about -| (0.12) ; famish- 
ing an argument similar to that found in the case 
of Jupiter, which is strengthened by a parallel 
observation of atmospheric belts. We consider 
it probable that Saturn is in a more advanced 
stage of planetary development than Jupiter, 
but that he is as yet uninhabitable ; and that his 
moons are the only members of his system which 
are at present capable of sustaining the higher 
forms of life upon their surfaces. The condition 
of Saturn is probably like that of the Earth in 
the era when our carboniferous rocks were being 
deposited froni the atmosphere and the water, 
which were thus purified for the use of the 
higher animals in the next geologic era. Under 
such circumstances it is useless to speculate on 
the views obtainable from the surface of Saturn. 
The inhabitants of that planet in the far distant 
future, when the Earth has chilled down into 
majestic death, will doubtless see the satellites, 
and perhaps others that have escaped our 
notice ; but they may know nothing of the mag- 
nificent rings which puzzled our astronomers for 
so many years. Those rings will, in all proba- 
bility, have broken up to form one or more addi- 
tional moons, before the advent of highly organ- 



MARS. 75 

ized beings on the surface of Saturn. Struve is 
said to have recently seen the obscure inner por- 
tion of the ring settle down upon, and spread 
over, the body of the planet. 

We find on the planet Mars indications of con- 
ditions very similar to those obtaining on the 
Earth's surface ; though differing widely in many 
important particulars. Mars is nearly of the 
same density as the Earth ; though, being less 
than 5000 miles in diameter, his volume and 
weight are but about -§• part of that of our globe. 
"We may infer from this that he has cooled a little 
more rapidly than the Earth, especially as he 
receives less heat than we do, being farther from 
the Sun. But we find indubitable evidences of 
land and water, and snow on his surface, and 
clouds in his atmosphere. His poles of rotation 
are seen to be capped with ice or snow, which 
increases or diminishes in bulk as the pole is 
turned to or from the Sun. Hence the processes 
of evaporation and rain- fall, melting and thawing, 
are perpetually going on ; as in the case of the 
Earth. The melting at the south pole of the 
planet, in particular, has been observed ; and it 
occurs rapidly, that pole being turned toward the 
Sun when the planet is nearest to him, and also 
nearest to the Earth's orbit. Mars was in this 
position in 1862 ; and was so near to us as to 
permit the principal features of his surface to be 
mapped out by Mr. Dawes. It has seas and 



76 



MAPS OF THE 



continents like ours, and yet unlike in their gen- 
eral distribution. The accompanying maps of his 
two hemispheres, which I prepared a year ago 
for the " Chicago Tribune," show the distribution 
of land and water on the surface of Mars. The 
most prominent of these have been named, and 
the letters refer to the names our astronomers 
have given to the more important continents 
and seas. We 
have no means 
of knowing 
how they are 
designated by 
the students of 
Erotography 
(Eros, Mars) 
who live on 
the planet. 

The shaded 
portions of the 
diagram rep- 
resent the land ; the white spots show the rela- 
tive distribution of the water. The upper part 
of each diagram represents the north, and the 
breaks in the bounding circles show the positions 
of the poles. Each pole is surrounded by a 
patch of ice, marking the middle of the polar 
regions. The following are the references : 

A. Dawes Continent. C. Cassini Land. 

B. Dawes Ocean. D. Delambre Sea. 




PLANET MARS. 



77 



E. De La Rue Sea. 

F. Fontana Land. 

H. Herscliel Continent. 
J. Maraldi Sea. 
K. Kepler Land. 



L. Lockyer Land. 
M. Madler Continent. 
K Tycho Sea. 
P. Phillips Island. 
P. Secchi Continent. 



A' comparison of the above diagrams with a 
hemisphere map of our world will show several 
important differences. On the Earth the land 

•lies in com- 
pact, though 
irreg ular, 
masses, and 
the tides of the 
ocean have 
free course, 
except where 
they pass be- 
tween islands, 
or through 
channels that 
separate isl- 
ands from the main land. The surface of Mars 
is marked by numerous seas of the bottle-neck 
form, and these run between continents and 
lengthy peninsulas; only one rounded island 
being visible, and that is probably a volcano. 
On Mars the land and water are nearly equal ; 
while on the Earth the waters cover nearly three- 
fourths of the entire surface. The land of Mars 
is of a ruddy color; and it is the reflection of 




78 CONDITIONS OF 

the solar' rays from this which gives the red 
appearance of the planet. The water is of a 
greenish hue (as seen through the telescope), and 
the latter fact indicates a condition similar to the 
waters of the Earth, which are blue or green 
according to distance from the shore. The appa- 
rent hue of the waters is undoubtedly modified 
somewhat by the passage of the rays of light 
through the Martial atmosphere, before they pass 
through "the ethereal void " to impinge on the 
aerial envelope which surrounds our Earth. 
Mars presents a very large extent of coast-line 
as compared with the Earth, and it is apparent 
from the diagrams that it is possible to travel by 
land to almost every part of his land surface 
without resort to navigation. 

Mars is, therefore, adapted as a residence for 
rational beings, like ourselves ; and it may be that 
they have attained to a higher stage of mental 
development than we have, for the double reason 
that the planet appears to have been habitable 
some thousands of years longer than our Earth, 
and also that the extremes of temperature are 
greater — the latter stimulating inventive inge- 
nuity, as in a lesser degree with ourselves. The 
length of the Martial day is about the same as 
ours, and the inclination of his axis to the plane 
of the orbit is nearly the same as in the case of 
the Earth ; but the eccentricity of his orbit is so 
great that if his nearest distance be represented 



LIFE ON MARS. 79 

by 5, his greatest distance from the Sun will be 
6, and he receives one third more heat and light 
in the former position than in the latter ; while 
the Earth differences of temperature are but as 
14 to 15. The annual range of temperature at 
any one place on the planet Mars will be one- 
fourth greater than with us ; and the equalizing 
effects of ocean currents must be very much less 
felt on that planet, owing to the peculiar distri- 
bution of land and water on his surface, and the 
comparative absence of ocean tides — Mars being 
unattended by a moon. Hence Mars has much 
less of atmospheric disturbance than we have; 
the seasons shading off gradually, from hot to 
cold, and from cold to hot again. But the 
amount of solar heat, and solar evaporation, 
must have a much wider range than on the 
Earth, owing to the great eccentricity of the 
orbit of the planet. This will also give rise to 
greater differences of extreme and average tem- 
perature in the two hemispheres than with us ; 
and, hence, give a possibility of far wider range, 
and much greater differences in the modes of 
existence, than are known on the Earth. From 
this we may infer that the number of classes and 
species of vegetables and animals is much greater, 
while the number of individuals of each order is 
smaller, on the surface of Mars than on that of 
the Earth ; and it is very probable that the ma- 
jority are monennial — having an existence lim- 
ited to one year of Mars life. 



80 THE OUTLOOK FROM MARS. 

Locomotion on Mars would be very easy to 
men possessed of our muscular strength, as the 
force of gravity is only about two-fifths of that at 
the Earth's surface ; and the loss of power by 
friction must be correspondingly reduced. If 
the inhabitants of Mars have no moon of their 
own, they can see ours with the naked eye, if 
blessed with vision as keen as ourselves ; they 
have probably never seen the planet Mercury, 
and may be able to see the larger Sun spots, but 
not the solar corona, being strangers to the phen- 
omena of an eclipse. They may catch occa- 
sional glimpses of Jupiter's moons, and see sev- 
eral of the planetoids, where we have never 
caught a sight of any other than Ceres and Yesta 
without the aid of the telescope. 

We have already indicated that Mars has 
nothing to compare with our tidal phenomena, 
owing to the absence of a moon. With us the 
attraction of the Moon is to that of the Sun as 
51 to 20. Hence, the magnitude of our tides 
being represented by 7, that due to the Sun 
would be 2. The greater distance of Mars from 
the Sun, and the lesser distance of his waters 
from the centre of the planet, will reduce the 
height of the tidal wave in his larger oceans to 
three or four inches ; while the tide in our open 
ocean is four feet. The rush of waters through 
the narrow inlets will be somewhat greater, 
though slight — just enough to keep up a mod- 



PHYSICAL CHANGES. 81 

erate circulation in the waters. With such a 
land contour on our Earth the greater tides 
would cause rapid changes in the plan of the 
continents. In Mars we have no very active 
cause of mutability in this direction. The per- 
manence of such an outline as is presented by 
Mars Would be practically impossible were he 
attended by a moon of considerable weight. 
Here we have one among numerous examples of 
" the eternal fitness of things " to their surround- 
ing conditions, 

In this lesser tidal flow, we have also an ab- 
sence of the forces which have produced such 
great changes in the Earth's surface, in cutting 
channels through what was once an isthmus, and 
the separating an island from the mainland. 
But, inasmuch as Mars exhibits a greater pro- 
pensity for channel-forming than is indicated in 
the case of our Earth, we can but conclude that 
the original volcanic action, which elevated the 
land masses above his mean surface, operated 
largely in lines of force, whereas the upheavals 
of the Earth were often effected in points ; as is 
attested by our numerous islandic formations: 
And, strangely enough, these elevating forces 
appear to have operated in the polar regions 
nearly parallel to the plane of the equator ; while 
in the equatorial regions these lines of upheaval 
are more nearly perpendicular to the direction of 
rotation on the axis. This irregularity of forma- 



82 MAES' METEOROLOGY. 

tion is undoubtedly due to the great eccentricity 
of the orbit of Mars ; the more important ruptures 
in the once thin crust, occurring near the time of 
the perihelion. 

It is also noteworthy that the positions of the 
ice formations indicate that the poles of Mars are 
the regions of greatest cold ; which is not the case 
on the Earth's surface, the point of minimum 
temperature in our Northern hemisphere lying 
ten or twelve degrees from the pole, toward 
the American Continent, while our magnetic 
poles show an equally wide departure from the 
poles of rotation. It is already known that the 
position of the magnetic pole is deducible from 
a study of the lunar motion; and it is highly 
probable that the positions of the points of least 
temperature will yet be traced to the same cause. 
Mars being unattended by a moon, there is, in 
his case, no apparent cause for difference in the 
average locality of the several poles of rotation, 
magnetism, and temperature. 

"We know much less of Yenus than of Mars ; 
but astronomers have discovered evidences of a 
dense cloudy atmosphere ; and irregularities on 
the outline, which are believed to indicate the 
existence of mountains twenty miles high. Yenus 
differs but little from the Earth in size or density ; 
and her day is about the same length as ours, 
giving a very small compression at the poles. 
Yenus is undoubtedly habitable. She receives 



LIFE ON VENUS. 83 

about twice as much heat and light from the 
Sun as we do, but her surface is not, necessarily, 
much hotter than that of the Earth, as her 
atmosphere may be adapted to the increased 
outer heat ; and, even if not so, the temperature 
is still below the upper limits of material organi- 
zation. ' Her atmosphere has been computed to 
be one-fourth more dense than ours ; and this 
agrees with the probability that the greater near- 
ness to the Sun produces much more evaporation 
from the .ocean than with us, and causes the 
peculiar clouded appearance of her atmosphere, 
which at once shuts out the direct rays of the 
Sun, causing him to be seldom visible, and pre- 
vents us from obtaining a knowledge of the dis- 
tribution of land and water on her surface. 
"Venus has no moon, and therefore no tides, in 
our sense of the term ; but her axis being inclined 
fully 55° from the axis of her orbit, her inhabi- 
tants are subjected to great irregularities of tem- 
perature in the different seasons, with great 
differences in the lengths of days and nights. 
And the changes of position ensuing from this 
phenomenon, bringing widely different parts of 
her surface under the Sun in rapid succession, 
must cause rapid variations of temperature as 
affected by atmospheric currents. The evapora- 
tion being so much greater, the trade winds must 
blow with hurricane velocities, and the general 
positions of the belts vary rapidly and widely ; 



84 life on mercury: 

while rain-falls must be frequent, spasmodic and 
heavy, causing swift-flowing rivers, and stupen- 
dous changes of land, outline, accompanied by- 
countless earthquakes and numerous volcanic 
eruptions. We may guess the inhabitants of 
Yenus to be short and stout, as befits those who 
have to do constant, sturdy battle with the ele- 
ments ; and to be possessed of little knowledge of 
the great universe without, owing to the diffi- 
culty of seeing through an atmosphere always 
surcharged with vapor. Hence they may know 
but little of the exact sciences, which, among us, 
have been cultivated largely in deference to the 
needs of astronomical research. We may infer 
also that their fruits and cereals are large and 
juicy ; and that the times of seeding and harvest 
come within an earth month of each other ; both 
being performed during that short interval in 
their brief summer, between the deferred spring 
gales and the early autumn tempests. 

Mercury is probably too near the Sun to be 
habitable by any but a very low order of beings ; 
especially as the great eccentricity of his orbit 
causes a change every six weeks from a position 
where he receives ten times as much heat and 
light as the Earth, to a point in the orbit where 
he receives only 4^ times as much heat and light 
as ourselves, or the reverse. It has been graphi- 
cally stated that this change of temperature is 
nearly equal to the difference between melted 



URANUS AND NEPTUNE. 85 

lead and frozen quicksilver; so that, whatever 
may be the absorptive properties of his atmos- 
phere, the change is probably too great to permit 
life of any but a low order on his surface. His 
atmosphere is very dense ; and it is not improb- 
able that Mercury is not yet cooled sufficiently to 
permit the formation of a solid crust, though 
some observers claim to have seen a mountain 
eleven miles high in his southern hemisphere. 

Of Uranus and Neptune we know so little, 
ow T ing to their great distance, that we are unable 
to form an estimate of their present adaptability 
to organic life on their surfaces ; though the anal- 
ogy justifies us in believing that they have been, 
are, or will be, the theatres of organized life. 
"We can compute that, with the same atmospheric 
medium as that which envelops our Earth, 
Uranus only receives one part in 368, and Nep- 
tune only one part in 904,«*as much heat and 
light as we receive from the Sun. But the 
atmospheric conditions in each case may be so 
ordered, that each receives enough of light and 
heat to sustain life on his surface ; for we must 
remember, as explained in the preceding lecture, 
that the intensity of the sensation is dependent 
upon the medium through which the force acts. 
If so, the view of the heavens from Uranus will 
be moderately interesting, as his sky is lighted 
up by four moons, though they can not shine so 
brightly as ours ; but the out-look from Neptune 



86 



must be blank indeed. The inhabitants of the 
outermost planet may be able to determine the 
parallaxes of a great many more of the fixed stars 
than we can ; but to them the Sun will be a very 
uninteresting looking object, scarcely twice as 
large as Jupiter appeared to us last winter, and 
none of the planets in the system, inside the 
orbit of Jupiter, will be visible. To the inhabi- 
tants of Neptune, our Earth, with its history of 
overwhelming interest to us, its innumerable 
scenes of joy and sorrow, its grand achievements 
in the realms of science, will be too insignificent 
to be noticed from its oldest brother. Well might 
the Psalmist exclaim — ""What is man, that 
Thou should'st be mindful of him?" 

We may dismiss briefly the planetoids which 
revolve between the orbits of Mars and Jupiter ; 
the number of which is anywhere from 112, 
known, to 150,000^yet to be discovered. The 
largest of these bodies — Ceres and Vesta — 
are scarcely more than 280 miles in diameter, 
and would cool down to the zero of life in Po- 
part of the time required for the Moon to become 
uninhabitable. Of the smaller ones there is still 
less necessity to speak ; they were all, probably, 
used-up planets, thousands of years ago ; and life 
was permitted on the surface of one of those 
bodies but for a very brief period. It would be 
highly instructive could we trace the record of 
one of those little worlds through a thousand 



AEROLITES AND COMETS. 87 

years of earth time ; it would present an epitome 
of the history of our planet for many millions of 
years. But it is a sealed book to us ; except as 
we can spell out the few characters on the exte- 
rior of the volume. No mortal eye may scan 
the hieroglyphics themselves — much less be 
permitted to decipher their hidden meaning, and 
add its lore to the fragmentary fund of human 
knowledge. 

Still less are the aerolites inhabited ; no life is 
sacrificed to the stern fiat of the law of attrac- 
tion, in the case of the millions of aerolitic bodies 
which fall to the Earth yearly, unless we except 
the case of one of the ancients, whose name has 
escaped me ; he is reported to have been struck 
dead by a stone falling from mid-air, which was 
probably an aerolite, though said to have been 
dropped by an eagle. He is the only man ever 
known to have come into collision with another 
world ; and the shock was fatal. We have still 
less reason to think it possible that the cometary 
masses are habitable. Their gaseous constitu- 
tion, and the terrific alternations of heat and cold 
to which they are subjected in a single revolu- 
tion, forbids the supposition. The nebulae are 
uninhabitable, like the comets ; affording no foot- 
hold for organized existence. 

We see, then, that of the untold millions of 
objects which the telescope shows us exist in the 
firmament, only a very few — a number small 



88 INVISIBLE WORLDS. 

enough to be told on the fingers, at twice — are 
probably habitable by any beings which require 
the organization of material atoms, as a medium 
for the exhibition of vital powers and functions. 
How vast must be the number of invisible worlds 
which do sustain life, in order to carry out the 
analogy suggested by a look at our own globe, it 
is impossible to tell ; or even to guess. But of 
one thing we may feel assured. "What we do 
see, even with* telescopic eye, is not more than a 
drop in the bucket, as compared with the bound- 
less ocean of existence that we can not see. Every 
leaf around us is teeming with life. Every pul- 
sation of the heart sends coursing through our 
veins millions of creatures, all organized to be, 
to do, and to suffer — genuine verbs of existence. 
Every mouthful of water we drink, or food we 
eat, involves the destruction of thousands of 
living beings ; and with every breath we draw 
we change the current of life to many an organ- 
ism. This world is a great theatre of vitality ; 
and we can not doubt that the number of such 
theatres of action is as great as, or greater than, 
that of the centres of light and heat ; which seem 
to have been established for the express purpose 
of enabling those unseen worlds to fulfill their 
mission. 

We are thus enabled to infer the conditions of 
existence on other worlds to-day ; but we have 
also seen that the conditions obtaining on any 



IMPONDERABLE FORCES. 89 

one body are dependent on those of other aggre- 
gations of matter. Changes in one produce 
effects on all. The attraction of the Earth has 
destroyed the axial motion of the Moon ; and the 
rotation of the Earth is slowly dying out as a 
consequence of the Moon's attraction on the 
Waters of our ocean. Looking out still further, 
we find correspondent influential changes in 
other bodies. The material particles which 
make up the mass of the Sun are in a state of 
incessant vibration ; and these vibrations give rise 
to the phenomena indicated by the names, light, 
heat, and electricity, which all appear to be but 
different expressions of the same force, accord- 
ing to the medium through which it ^cts. "We 
can gain an idea of this convertibility of function 
by exciting to rapid motion the atoms of a mass 
of matter ; either by friction, as in the electrical 
machine, or by inciting chemical change, in the 
galvanic battery. If we allow the excitement, 
thus produced, to pass along a piece of wire, 
which offers no resistance to the flow, we have 
an electric current. If we interpose what is 
called an imperfect conductor, the flow of the 
current is partially arrested, and gives rise to the 
sensation of heat. If we cause the current to 
flow from one point to another, through space, 
without affording a conductor, it produces light. 
The force which is evolved by the Sun particles, 
in moving among each other, is electricity at his 



90 SUN SPOTS AND STORMS: 

surface ; traveling through the void, which pre- 
sents nothing but an extremely tenuous ether as 
a conductor, it is light ; communicated to us by 
imperfectly conducting matter in the atmosphere, 
it gives heat. 

And we find that this force varies, not only in 
the form of its expression, with the medium 
through which it acts, but varies also in its 
intensity, in sympathy with the positions of other 
masses of matter. The changes which mark the 
seasons are caused by the varying position of the 
Earth's axis ; and the minor changes, occurring 
almost daily and hourly, are due to altering con- 
ditions of our atmosphere. But the force of the 
solar light and heat is also variable. The spots, 
which we saw in the preceding lecture are evi- 
dences of violent storms in the Sun, have a regu- 
lar cycle of about eleven years, corresponding 
nearly to the revolution of Jupiter. Thus : a 
very few spots were visible in 1856, and the 
number increased in 1859 and 1860 ; observations 
being made of 297 in the latter year. From this 
time the number decreased for about five years, 
and again increased to 1870, when the number 
seen was greater than at any time during the 
century. Jupiter is, by far, the largest planet in 
the system ; and it is but natural to suppose that 
he produces the greatest effect. But Yenus is 
also found to exercise a powerful influence in the 
formation of spots ; they being always most nu- 



THEIR CAUSES. 91 

merous when Venus and Jupiter are on the same 
side of the Sun, both operating in the same direc- 
tion. It is also considered probable that there is 
a greater cycle of 58 to 60 years, corresponding 
to five revolutions of Jupiter and two of Saturn ; 
and a still larger cycle of 168 years, measured 
by two revolutions of Uranus and one of Hep- 
tune. As the maximum times of these different 
cycles coincide or interfere with each other, the 
relative extent of the Sun storms will vary ; just 
as the height of the tides in our ocean is greatest 
when the Sun and Moon are acting together (on 
the same line), and least when their attractions 
are pulling at right angles to each other. I 
pointed out the fact that near the time of the 
maximum exhibition of Sun spots in the Spring 
of 1870, the Earth, Sun, Jupiter, Mars, and 
Venus, were all nearly on one straight line in 
the heavens. 

These planetary movements cause storms in 
the Sun, just as Earth storms and tides are pro- 
duced by the varying positions of the luminaries ; 
and can be calculated on with certainty before- 
hand. The astronomical world had long known 
that 1870 would be a maximum year. 

And these changes, though great, fully one 
part in 130 of the whole apparent surface of the 
Sun being covered by black spots last year, seem 
to be but small compared with those which have 
occurred in the past. Abul Farajius, an Ara- 



92 variable stars: 

bian historian, tells us that in the 17th year of 
Heraclius, half the body of the Sun was eclipsed, 
continuing for eight months ; this corresponds to 
the year 626 of the Christian Era. It is more 
than probable that the great darkness at the time 
of the crucifixion was caused by an enormous 
Sun spot ; as there are grave difficulties in the 
way of supposing it to have been produced by 
an eclipse of the Sun. 

We find similar changes, in the present age, 
in the fixed stars. The periods of more than 100 
variable stars are known ; and there are many 
others known to be variable, the periods of which 
have not been ascertained. The star Algol (Beta 
Persei) changes from the 2-J magnitude to the 
4th, and back again, in 2.9 days. It shines as a 
star of nearly the 2nd magnitude for 2 days 13-J 
hours ; then loses its light for 3-J hours ; then 
increases in brilliancy for 3-J- hours, and regains its 
former brightness. It is now believed that this 
phenomenon is due to the passage of an opaque 
attendant across his disc. But the star Mira 
(Omicron Ceti), or the Marvelous, has a period 
which can not be accounted for in this way ; and 
so have very many others. Mira is usually seen 
as a star of the 2nd magnitude for about 15 days, 
then decreases in light for three months, at the end 
of which time it is only of the 11th magnitude, 
and can scarcely be seen for five months, even in a 
good telescope. It then increases in brilliancy 



93 



for another three months ; the whole cycle having 
been performed in 331f days. This period is 
subject to variation, and so is the amount of light 
received from the star, by us, at different times 
of maximum ; it is sometimes no brighter than a 
star of the 4th magnitude, when at the brightest 
phase of one of its periods. In this star, and in 
many others of the same class, we have very 
probably a similar set of conditions to those 
existing in the case of the Sun, but on a much 
larger scale. Balfour Stewart has suggested 
that, inasmuch as the Sun's brightness increases 
on the approach of a planet, and especially in 
that part nearest the planet (probably due to the 
reflection of light as well as to gravitative distur- 
bance), these variable stars have large planets 
revolving around them at comparatively small 
distances, and that the brightest part of the sur- 
face is turned toward the planet. If the planet 
have a prolonged elliptical orbit of revolution, 
then the star will be very bright during 
only a small part of the period. And we may 
add to the theory of Stewart that if the axis 
major of the orbit has also a rapid movement, 
like that of the Moon, this fact will account for 
the differences exhibited in successive cycles, as 
the bright side will sometimes be turned toward 
us and sometimes from us, at the time of the 
actual maximum. It is not true, however, that 
the greatest brightness occurs at the time of 



94 STARS OF LONG PERIOD. 

nearest approach by the revolving body. The 
intensity of luminous disturbance appears to be 
rather due to planetarj^ configuration than to 
mere distance. 

Our Sun is a variable star ; like Mira. 

A remarkable example of another class of 
variable stars is found in Eta Argo, situated only 
31° from the South pole; and therefore too far 
South to be seen in this latitude. It has a peri- 
odical change, between the 1st and 4th magni- 
tudes, in a space of 46 years. And it is singular 
that a nebula surrounding it appears to be grow- 
ing richer at the expense of the star ; increasing 
in brightness as the star diminishes in lustre, and 
also undergoes a marked change in form. 

A new star appeared suddenly in 1572, in the 
constellation Cassiopeia, and was visible for 17 
months ; its light being at one time so brilliant 
that it was equal to that of the brightest of the 
planets, and was visible at noonday. It sud- 
denly disappeared, and was not afterward visible. 
But we find it recorded that in the years 1264 
and 945 A.D. a similar appearance was noticed 
in the same region. These three dates are sep- 
arated by intervals of 308 and 319 years ; hence 
it is considered as probable that the star will 
re-appear before the year 1900. If so, this star 
presents us with a case of a variable of very 
long period, which is very bright at its maxi- 
mum, and fades, even beyond telescopic vision, 
during the greater part of its cycle. 



STAR CONFLAGRATION. . 95 

But there are some stars which seem to vary 
from other than mechanical causes. The most 
notable of these is one known as Tan in the 
Northern Crown. It was a telescopic star, of the 
9th magnitude, previous to May, 1866. In that 
'month it suddenly became visible to the naked 
eye ; and on the 12th instant was nearly equal in 
brilliancy to a star of the 1st magnitude. On 
the 14th it was only of the 3rd magnitude ; and 
it rapidly faded away to its original obscurity. 
Examination with the spectroscope led to the 
inference that this sudden apparition was caused 
by a genuine conflagration of hydrogen gas in 
the atmosphere of the star. Now; we "know 
that immense aggregations of hydrogen are pres- 
ent in the Sun ; and it is not impossible that a 
similar phenomenon has occurred in the past, or 
may occur in the future, in the centre of our 
system ; though it is not probable, owing to the 
apparent absence of oxygen. What would be 
the result of such a change in the Sun ? It would 
undoubtedly cause such an immense increase in 
the temperature of the Earth as to revolutionize 
our globe, completely, killing off most of the 
plants and animals now existing, calling out 
mighty eruptions of the fluid interior, and 
leaving the world a wreck ; perhaps to be peo- 
pled by new forms, adapted to the altered condi- 
tions of our planet. It is not the province of 
true science to attack or defend the truth which 



96 THE END OF THE WORLD. 

is revealed ; but we can not resist the thought 
that possibly this is the way in which the Scrip- 
ture w^ill yet be fulfilled. A conflagration of 
hydrogen in the Sun, like that observed in Tau 
Coronse, may be the agency chosen to cause the 
heavens to gather as a scroll, the elements to 
melt with fervent heat, the Sun and Moon to 
seem to turn to blood, and bring about the new 
firmament, and the new Earth whereon dwelleth 
righteousness. 

We have no geological record of such a con- 
flagration in the past ; but we have abundant evi- 
dence of the fact that the minor changes in the 
condition of that variable star which we call the 
Sun, are not only caused by planetary motion, 
but have a reflex influence on planetary condi- 
tions. In my theory of the " Sun-spots and their 
Lessons," I have shown how the Earth was 
affected in its meteorological conditions by those 
phenomena in 1870 ; and the deductions have 
been accurately borne out by the observed facts. 
The spectroscope shows us that the dark rays 
emit comparatively little heat ; but are prolific in 
the elements of chemical and electrical change. 
The result of Sun-spots last year was a reduction 
of about 2° in the amount of heat supplied to the 
whole globe — of earth, water, and air. This 
caused a reduction, of not less than four inches in 
depth, in the amount of water taken up from the 
ocean by the evaporating power of the Sun, and 



RESULTS OF SUN SPOTS. 97 

the necessary consequence of this diminished 
cloud supply was a diminished rain-fall all over 
the civilized globe ; the season was one of the 
driest ever known, and the effects were wonder- 
fully marked in the yield of the crops, the course 
of commerce, and the welfare of nations. Our 
corn crop was immense, as a consequence of the 
dry time, which almost totally suspended traffic 
on the Illinois river, and its connecting canal ; 
and we can not say how much the course of 
events in Europe would have been changed, if 
the French gunboats had found water enough in 
the Rhine to enable them to operate against the 
Prussians. The effect of the diminished heat 
supply to the globe was not, however, a cold 
summer. The rain-fall being reduced nearly 
one-half, there was much less water to be evap- 
orated from the land than usual — water taking 
up 1,100° of heat in passing from ordinary tem- 
peratures to a state of elastic vapor. Hence the 
slightly decreased heat received from the Sun 
actually produced a greater heat to the senses ; 
not being carried off in the ordinary way into 
the upper regions of the atmosphere. The effects 
of this lack of evaporation are shown in the deserts 
on which rain never falls, because the cloud- 
bearing winds are intercepted by surrounding 
. mountains. The thermometer often marks 130° 
in the Desert of Sahara, though the average tem- 
perature in that latitude is not more than 84°. 
5 



98 OTHER STAR CHANGES. 

Changes of equal magnitude were doubtless 
caused in tiie other bodies of the system, during 
the past year, by the Sun-spots; and greater 
Sun-spot exhibitions in the past have undoubt- 
edly wrought far greater changes on the surface 
of our planet than those which occurred in 1870. 

Many of the fixed stars exhibit changes of 
color, without remarkable variation of bright- 
ness. Sirius was spoken of by the ancients as 
of a fiery red, but was recently white, and is 
now ass Liming the green color. Capella was also 
a red star formerly, afterward yellow, then white, 
and is now turning blue. These phenomena 
prove to us that extensive changes are in pro- 
gress, the character of which we are as yet 
unable to determine. 

These minor cycles of change, though great in 
themselves, are very small when compared with 
those indicated in the facts we have considered 
in this lecture. We have seen that the Moon 
w r as once like the Earth of to-day ; and that both 
were once like the Sun, giving out light and heat 
as glowing masses of incandescent matter. We 
find nebulous aggregations which appear to be, 
as yet, uncondensed into the more solid form 
assumed by planets, Sun and stars : and we have 
discovered in all some of the very same chemical 
elements which make up a large proportion of 
the mass of our Earth. Philosophers have taken 
up these, and other, facts ; and traced back the 



THE PRIMEVAL CHAOS. 99 

analogies presented, to what appear to be legiti- 
mate conclusions. We have not time to dwell 
on the successive steps of the reasoning process, 
but will present in brief the past history of the 
Universe, as it has been read out from present 
facts ; just as the geologist has traced the past 
history of our own planet, from a study of the 
records that are deep graven in the rocks. They 
exist there in a language which though not alpha- 
betic is universal, and can be understood by the 
men and women of every clime — into whatever 
tongue they may be obliged to translate those 
records in order to communicate the knowledge 
to their neighbors. 

The space wiiich we now call the Universe 
was once filled with matter in a state of extreme 
tenuity, fully three thousand million times less 
dense than atmospheric air at the Earth's surface, 
or two and a half million million times less dense 
than water. This was the original chaos. The 
matter was equally distributed, because no laws 
of aggregation existed. The establishment of 
the law of attraction of gravitation w T as the first 
great creative act. 

If this law were first impressed upon a few 
adjacent atoms, they would at once move toward 
each other, and form a mass ; if the same law 
w r ere then instituted throughout the Universe, 
all the surrounding atoms would at once be 
attracted toward the first formed nucleus, the 



100 PROBABLE HISTORY OF 

position of which would be preserved, because 
the attraction would be equal in every direction ; 
and for the same reason the gathering particles 
would form a globe-shaped aggregation. The 
mutual friction of the atoms would generate the 
force that would cause heat as the first effect of 
the compression ; then electrical excitement, as 
the atoms came more closely together ; then 
light, as the vibrations of the mass were commu- 
nicated through the partially cleared spaces out- 
side the aggregation. 

Millions of these centres and aggregations 
might be formed, through the immense void. 
We may take one of them in our mind's eye, and 
glance at its subsequent history. The inevitable 
tendency of the mutual flow of atoms would be 
to produce a whirling motion of the mass ; as the 
flow of water in a funnel is always accompanied 
by a rotary movement. The attraction still 
operating, the interior atoms would be forced 
nearer to each other by the pressure from with- 
out ; but this would be partially counteracted in 
the equatorial portions, by the rotary movement, 
and the combination of forces would produce an 
ellipsoidal mass — flattened at the poles in exact 
proportion to the velocity of rotation on the axis. 
These changes would continue till an equilibrium 
was established ; the centrifugal force at the 
surface of the equatorial part being equal to the 
force of attraction toward, the centre. 



WORLD CREATION. 101 

During all this time the action of light and 
heat, on the particles of matter, would aggregate 
them into smaller groups, forming chemical 
atoms, possessing different properties ; and then 
would begin the play of chemical affinities. 
These secondary atoms, combining in various 
proportions, would form definite substances, giv- 
ing rise to subordinate centres of attraction, about 
which the adjacant atoms would gather. The 
movement toward the new centres would produce 
a rotation of each mass, as in the first instance; 
while the motion around the original centre 
would continue, becoming a revolution in the case 
of each individualized mass. The tendency of 
the interior portions of the original aggregation, 
to move with greater angular velocity than those 
farther from its centre, would lead to its separa- 
tion into rings, or bands. The separate parts of 
each ring might aggregate into one planet, as in 
the case of Jupiter and Mars, or into several 
bodies, as in the case of the planetoid family 
revolving between the orbits of those two greater 
planets ; some of these rings doubtless exist still, 
without aggregations large enough to be visible 
to us, except when they come within the limits 
of our atmosphere. 

The same process of throwing off rings might 
be repeated in the case of each planetary mass ; 
and these secondary rings would either revolve, 
as such, around the planet — as is now the case 



102 WORLD FORMATION. 

with .the rings of Saturn — or form smaller 
bodies by aggregation — as in the case of our 
Moon, and the satellites of Jupiter. The liabil- 
ity to this division would be in proportion to the 
magnitude, and the consequent difference be- 
tween the angular velocities of the interior and 
exterior portions — the actual velocities being 
nearly equal, as being produced by the same 
moving impulse toward the centre. Accordingly 
we find that the largest planets have the greatest 
velocity of axial rotation, and several moons ; the 
smaller ones have none at all. But each may be 
a centre of revolution to millions of bodies too 
small to be discerned ; only the smaller planet- 
oids being actually destitute of attendants. 

The Earth, as thus formed, would be, at first, 
a much larger mass than at present ; her circum- 
ference extending far beyond the present orbit 
of the Moon. For millions of years after our 
satellite was thrown off, the Earth would glow 
at more than a white heat, as a result of the 
mutual compression of its component matter. It 
would cool rapidly at the surface ; the lighter 
particles taking the outer position, by virtue of 
their less specific gravity, and forming an atmos- 
phere of vapor. Through a long course of ages 
the cooling process would continue, the surface 
gradually hardening into solid matter, but be- 
coming fissured by contraction, and falling into 
the fiery sea, whose commotions lifted up other 



UNFORMED MATTER. 103 

portions of the crust, forming continents and isl- 
ands. As the irregular surface became cooler, 
the vapors in the atmosphere would condense 
into water, forming seas ; and then the air and 
water, acting on the surface of the granitic crys- 
tal, would gradually wear away the material from 
which the aqueous rocks were afterward formed, 
and a foothold produced for the first forms of 
vegetable existence. The subsequent part of our 
wonderful Earth history is written in the rocks ; 
it is the province of the geologist to trace it out. 

Thus, all the visible and invisible objects in 
the Universe were formed from the one homoge- 
neous material. 

Till recently it was thought that the regions of 
space were swept clean by the attractions of those 
greater aggregations which we can see ; but we 
now know that what is called space is yet com- 
paratively full of material particles. Unnum- 
bered millions of aggregated atoms still course 
about within the bounds of the solar system ; 
and besides these the whole space is full of unat- 
tracted matter, yet unformed into even the small- 
est masses, which sustains much the same rela- 
tion to the planetoids as the air does to the motes 
that float in it, as revealed by the presence of a 
sunbeam. There is an old saying, to the effect 
that " Nature abhors a vacuum." It would prob- 
ably be impossible to exhaust the interplanetary 
spaces ; just as it is impossible, by the most per- 



104: ALL COMPOSED OF 

feet air pump ever invented, to form a comp]ete 
vacuum on the Earth's surface. 

Indeed ; it is probable that this unformed 
matter, the existence of which has been already 
demonstrated by the shortening of the period of 
Encke's comet to the amount of three days within 
the past eighty years, and which doubtless acts 
in the same way on the more dense planets, but 
to an extent not yet appreciated, has other, and 
very important functions. The diffusion of Sun- 
light in the atmosphere has recently been shown 
to be directly due to the presence of the motes 
floating in the aerial envelope of our globe ; as I 
announced in March, 1870, several months be- 
fore the fact was stated by Professor Tyndall. 
And there is reason to believe that the same office 
is performed in the interplanetary spaces by the 
asteroidal matter, while the propagation of the 
ray in a right line is due to the presence of the 
ether, or unformed matter; and it will yet be 
proved that not a single ray of absolutely unpo- 
larized light ever reaches our eyes. The theory 
of the polarization of light requires some modifi- 
cation to make it harmonize with the facts. 

This ether, and these planetoidal masses, 
whether specks or lumps of matter, are all com- 
posed of the very same element, or elements, as 
those which make up the sum of the planets and 
the stars. It is only the same matter, existing 
under different conditions ; and it is idle to dream, 



THE SAME ELEMENTS. 105 

as some liave done, of the existence of an ether, 
like -that of the interplanetary spaces, existing 
between earth atoms, to account for the phenom- 
ena of heat. All that we know of the constitu- 
tion of matter tends to indicate that there is 
really but one original element, though we enu- 
merate sixty-four : and I believe it w T ill yet be 
discovered that the diverse elementary atoms 
differ only in this, that each class of atoms has 
its own capacity for specific heat, being formed 
of groupings of the original particles in such a 
way that differing quantities of heat excitation 
are required to produce the same amount of heat- 
movement in the atom How this property was 
communicated w r e may never know; but it is 
not difficult to conceive it as the result of atomic 
formation at different stages in the cooling pro- 
cess. The atoms of each of the so-called chemi- 
cal elements have a separate rate of thermal 
vibration ; and the admission of this theory 
affords an ample reason for the display -of 
diverse properties. It will be remembered that 
each element gives lines in the spectrum which 
are only distinguished from the rest by specific 
lengths, and rapidities, in the arcs of vibration. 
"We may add, too, that this theory will enable us 
to account for the differences of atomic constitu- 
tion in bodies formed from the same mass ; and 
will also obviate the objections recently made 
to the igneous origin of the primary rocks. 



106 HISTORY OF 

We can not help being struck by the fact 
that the Universe presents to our view almost 
every different stage of growth and decay. The 
gaseous accumulations of matter, which we call 
nebulse, are in the earlier periods of existence — 
unborn suns. The Sun and stars are cooling 
bodies ; and will require millions of years to 
enable them to reach conditions similar to those 
of the Earth to-day. The cometary orbits lose a 
portion of their eilipticity with every revolution, 
and will settle down into staid members of the 
planetary family in the far distant future. The 
Moon has passed through the stage of active 
existence, and is going through her period of 
decay. The planetoids, which are continually 
falling to the Earth, and to the other planets, are 
bodies whose independent missions have been 
accomplished ; they have yielded up their sepa- 
rate identities, and gone to form portions of 
other and larger worlds. Pursuing this analogy 
to its legitimate sequel, we see, in the vast future, 
suns losing their light, and planets dying out 
from cold : we see moons falling to planets, and 
planets falling to suns ; and suns, again, subsid- 
ing into larger aggregations of matter. All this 
must occur in obedience to the law of attraction 
of gravitation ; because that force is constant, 
while its counterpoise, heat, is indubitably suscep- 
tible of decrease by radiation. We may go fur- 
ther. We may say that heat, itself, is but the 



THE UNIVERSE. 107 

effect of .gravitation ; and that, though the effect 
is at present equal to the cause, yet the cause is 
greater than the effect, in this respect, that the 
cause is perpetual, while the effect is evanescent. 
All the phenomena of motion, of heat, of light, 
of life, are traceable to the operation of this one 
great, incomprehensible force which we call 
attraction. All the phenomena must ultimately 
cease, by virtue of the operation of this force ; as 
the forces that produce and sustain human life 
for a brief period, are themselves the real causes 
of that which we call natural death. 

It is even possible to wing the flight of human 
thought over, and beyond, the countless stretch 
of ages which will measure the duration of the 
visible Universe. We can not absolutely know, 
but we may reason out from analogy, the idea, 
that a new Universe may be evolved from the 
general wreck ; and that without a new exercise 
of Creative energy. The concussion of such im- 
mense masses of matter as those into which the 
penultimate cosmos will be resolved, may gener- 
ate heat enough to redistribute the vast concourse 
of matter into its former diffused chaos, and per- 
mit the processes of condensation and formation 
to commence anew. And indeed, we know not 
but that our Universe may be only one of a vast 
series of such successive creations — a far down 
link in the mighty chain of involution and evolu- 
tion of material forms and forces, which is eternal 



108 TYPES OF 

to our finite minds, inasmuch, as we can not even 
guess at its possible limitations ; though it be 
still subordinate, in function and duration, to the 
Great First Cause, whom men call God. And 
let not this thought be deemed impious ! We 
sin not in endeavoring to grasp a scintillation 
of the Omniscience which beams on the throne 
of the Eternal ; we blaspheme only when we 
assume to sit on that terrible throne as a judg- 
ment seat, and dare to say that He hath not 
ordered all things well. 

Man has been called the microcosm — an 
epitome of the Universe. The individual who 
first gave shape to that thought was probably 
unable to comprehend its full scope. In a men- 
tal relation, man is the image of his Creator; 
physically considered, he is a type of the Uni- 
verse, through all the phases of growth, maturity, 
decline and extinction. Like him, the Great 
Universe is permanently impermanent. But the 
same is true of every part of the great whole. 
The plant gathers material from the soil and the 
atmosphere, pushes forward into life, attains to 
maturity, withers, dies, and rots away into thin 
air. The human body passes through a similar 
consecution of growth and decay — of formation 
and dissolution. Families of men have their 
periods of existence, but of longer duration ; 
nations pass through the same phases, but occupy 
still longer periods in the history of their distinct 



THE COSMOS. 109 

existence. As it is with nations, so with types 
of existence ; and as with types, so with the con- 
ditions under which they exist. These condi- 
tions, again, form but items in the history of a 
world formation, as the rotation of a planet on 
its axis is an item in the journey around the 
Sun. So the history of a world is but a part, 
and an ejjitome, in the history of a system; and 
that of a Universe. In all we see the signs of 
constant growth, up to certain limits ; then a 
staid maturity ; then an old age ; then death. 
It is true of the Universe as of man — we all do 
fade as a leaf. All wax old as doth a garment. 
Only one being exists of whom it can be said : 

" Thou art eternally the same, 
Thy years shall not fail." 



I hare been asked : How do the conclusions 
stated in these lectures, in reference to the crea- 
tion and dissolution of the Universe, and other 
deductions made by scientific men, harmonize 
with the teachings of the Bible ? and, if there be 
a disagreement, how shall we decide ? I answer : 

The two appear to disagree, in many important 
respects ; and a storm of controversy on the sub- 
ject has raged in the Christian world, with a few 
occasional lulls, ever since Copernicus announced 
that the Earth is not the centre of motion of the 



110 



visible Universe. But it is worthy of remark 
that the debate was far more violent and bitter a 
few score of years ago than it is to-day ; and its 
violence abates in exact proportion to the pro- 
gress of man in the study of the physical sciences, 
and in a critical knowledge of Bible meanings. 
The more w r e know, the less of disagreement do 
we find between the teachings of the Bible and 
the results of scientific research. 

All truth is consistent with itself; but if we 
find two assumed truths which appear to be 
inconsistent, it is no more probable that one of 
the assumptions is false, than that we have failed 
to understand one or both of them. 

It is also true that differences of opinion arise 
much oftener from a want of agreement as to the 
precise meanings that should be attached to differ- 
ent statements, than on account of a radical dis- 
agreement in the statements themselves. 

The generally received acceptations of the 
statements made in the first chapter of Genesis, 
do not harmonize with our geological theories. 
But that fact does not warrant the infidel conclu- 
sion that the Bible is an untrue record ; neither 
should it prevent us from studying the book of 
Nature. There is a mistake somewhere ; but it 
probably lies with those who first make up their 
minds that the Bible teaches this or that, and 
then anathematize all who will not accept their 
interpretation of its language. 



THE BIBLE. Ill 

The Bible was evidently not intended to be a 
teacher of physical science. The references made 
in that volume, to physical facts, are couched in 
the idioms best understood by the peoples who 
lived in the times and places where its several 
books were written. Even to-day, WE speak of 
sunrise and sunset, though we know very well 
that the Sun does not move to cause either of 
those phenomena. No one understands the Bib- 
lical allusions to " the four corners of the Earth," 
or its " firm foundations, that can not be moved," 
in any other way than as popular phraseology. 
Similarly no well-informed person now believes 
that " the Sun stood still upon Gibeon," at the 
command (or prayer) of Joshua, though he may 
accept the miracle of an extended day. And, 
yet, we have just as much warrant in the Bible 
for assuming that the Earth is the centre of the 
solar system, as we have for believing that the 
Earth, Moon, Sun, and Stars, were all created, 
out of nothing, in six days of twenty-four hours 
each. Indeed, Moses does not tell us that matter 
was formed from nothing; he simply says that, 
" In the be^innino; *" * • * the earth was 
without form, and void" — which is just what 
science teaches to-day. To create is to fashion, 
to shape, out of previously existing material. 

A great proportion of the creed called " Chris- 
tian" is falsely assumed to be found in the 
Bible ; it really originated in confessedly human 



112 



productions — from the writings of the Fathers, 
down to Milton's Paradise Lost. We can not 
find within the covers of the Bible a hint that 
the sacred volume was intended to be a teacher 
of Science, though we do find its uses defined. 
St. Paul tells Timothy that the Scripture is 
" profitable for doctrine, for reproof, for correc- 
tion, and for instruction in righteousness ; that 
the man of God may be perfect, (and) thoroughly 
furnished unto all good works." In the two sec- 
tions of this inspired volume we find only two 
great fundamental truths, a belief in which was 
insisted on ; the Old Testament anathematizes 
those who deny or forget the God of Israel ; the 
New Testament teaches that Jesus is the Christ. 
The latter truth was the only one to which the 
Eunuch gave assent as a preliminary to his bap- 
tism by Philip. Indeed it is well for the Christian 
world that the prophecies are the only portions 
of the book on which the Scriptures themselves 
forbid ns to put a private interpretation. If it 
be a sin for scientists to dispute the alleged mean- 
ings of a few Scriptural passages, which have no 
important bearing on Christian faith or a godly 
life, then there is not a church in existence but is 
a hundred times more guilty of the crime of 
"wresting the Scriptures"; and the verdict of 
guilty would be pronounced against every one of 
them, by the unanimous voice of all the rest. 
It may be claimed that the philosophers of our 



SCIENTIFIC TRUTH. 113 

age are no better agreed than the churches ; that 
the knowledge of to-morrow may largely modify 
many of the deductions of to-day, as the re- 
searches of this generation have demolished 
much that was accepted as truth in the past. 
We admit this; and claim that the fact is the 
best guarantee of ultimate wisdom as a result of 
honest, fearless investigation. "We are sure of 
very few facts or truths, yet, in comparison with 
the great mass of facts which yet remain to be 
mastered, and of truths yet to be patiently rea- 
soned out. The present state of scientific knowl- 
edge may be compared to the prima^ state of 
ossification in the unborn child. Bone com- 
mences to form at several detached points, and 
the growth has proceeded to a considerable 
extent before the extensions from these centres 
meet each other, and give the true skeleton. So. 
we know a great many isolated facts, and have 
reasoned out a few principles; but we are far 
from having reached the stage of development 
where we can take a bird's-eye view of things, 
and trace out their mutual connections and inter- 
causations, as " parts of one harmonious whole; 
whose body Nature is, and God the soul." 

In the book of revelation, and the book of Na- 
ture, we have two works which we believe to be 
the productions of one Author. For both we 
may claim that the difficulty of understanding 
them is the best proof of their divine origin. 



114: CONSISTENCY OF 

Any mere human work would have been mas- 
tered in less than one thousandth part of the 
time that has been spent in the attempt to com- 
prehend all that is written in either of those two 
volumes. The hieroglyphs of India, Egypt, 
and Assyria, of which the characters and the lan- 
guage were alike unknown, have been read out 
within the past hundred years; whereas these 
Divine books contain many thousands of mys- 
teries yet undeciphered, though they have been 
studied for scores of centuries. 

Believing this, we can but consider it our duty 
to study both ; and our high privilege to be per- 
mitted to do so. The intense mathemaphobia 
exhibited by some theologians can only be ac- 
counted for by supposing that they believe the 
book of Nature to have been written by the father 
of lies, for the express purpose of leading men 
astray. 

"We may feel assured of this : He who created 
all has made nothing in vain ; nothing that he 
did not intend to be used ; not a single talent that 
was designed to be buried in a napkin. The gift 
of reason was conferred on man that he might 
study the Great Author of the Universe in His 
works, and build himself up into a closer mental 
likeness of Him who knoweth all things. We 
have not yet progressed far enough in either 
department of the investigation to be able to 
make a dogmatic comparison of notes. But we 



TRUTH. 115 

are justified in believing that tlie Source of all 
Truth can not be inconsistent with Himself; and 
that, if we are ever able to grasp the whole truth 
of Revelation and of Nature, we shall see that all 
is in perfect harmony — just as we now know 
that the two opposing forces, known as the cen- 
tripetal and the centrifugal, originated in the one 
force which we call the Attraction of Gravitation. 



NOTES. 

Pages 17 and 105. The number of chemical elements absolutely 
known is sixty-four. The existence of three or four others is supposed 
rather than ascertained. 

Page 20, line 26; for this solar spectrum, read the solar spectrum. 

Page 31. The calcium light is the most intense we can produce, 
except the electric light. The limit of the latter is not known. The 
electric spark has been made to give a light nearly sixty times more 
intense than the calcium, or only two and a half times less intense than 
the sun light. 

Page 37. The chemical action of the sunbeam is now believed to be 
principally due to the presence of chromium, titanium, and magnesium 
in the sun. 



ANNOUNCEMENT. 



I have now, nearly completed, the material for a work 
on Astronomy, of which the following are the prominent 
features : 

Vol. i. Full and comprehensive star maps, engraved 
in the very best style, and in such portable form as to be 
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lists of interesting telescopic objects, with appropriate 
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will, however, be printed on first-class paper. 

Vol. 2. The methods of ascertaining the distances and 
dimensions of the heavenly bodies, explained so that 
everybody can understand the processes. The laws of 
world motion, similarly simplified, and the movements 
of earth, moon, planets, and stars explained, with the 
resulting phenomena. Star chemistry, and the biology 
of the universe, discussed somewhat more fully than in 
the preceding pages. 

Everything will be brought down to the latest date, 
and reduced to the simplest possible form ; so that he 
who runs may read, and all who read may understand. 

I wish to produce a work which will be a credit to the 
West, and to this end propose to publish it by subscrip- 
tion. If I obtain the names of subscribers for five hun- 
dred copies I will put the book to press. If the required 
encouragement be not forthcoming, I shall conclude the 
book is not wanted. 

I, therefore, invite orders, for one or more copies, from 
those interested in furthering so important a work, prom- 
ising to pay the retail price, not exceeding ten dollars 
per copy, on delivery. In return I promise that it shall 
be worth the money. 

E. COLBERT. 

Address, Chicago Tribune, 



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